The Phantom Airman by Walker, Rowland

[Illustration: "It was as though the mighty concussion had blown a hole in the universe."--_Page_ 245.]

THE PHANTOM AIRMAN

BY

ROWLAND WALKER

AUTHOR OF "DASTRAL OF THE FLYING CORPS," "DEVILLE McKEENE, THE BRITISH ACE," ETC, ETC.

S. W. PARTRIDGE & Co. 4, 5 & 6, SOHO SQUARE, LONDON, W.1

MADE IN GREAT BRITAIN _First Published_ 1920 _Frequently reprinted This Impression issued_ 1931

*CONTENTS*

CHAPTER

I. The Secret of the Schwarzwald II. The Wonder ’Plane III. "Tempest" of the Aerial Police IV. A Midnight Consultation V. The Aerial Liner VI. An Up-to-Date Cabin Boy VII. A Duel with Words VIII. Sons of the Desert IX. The Phantom Bird X. The Brigand of the Eastern Skies XI. The Air-King’s Tribute XII. The Maharajah’s Choice XIII. The Missing Airship XIV. Betrayed by the Camera XV. Diamond cut Diamond XVI. The Ghostly Visitant XVII. The Watchers XVIII. "Live Wires" XIX. The Devil’s Workshop XX. "Hands Up!" XXI. The Coming Fight XXII. An Aerial Duel

*THE PHANTOM AIRMAN*

*CHAPTER I*

*THE SECRET OF THE SCHWARZWALD*

Rittmeister Heinrich von Spitzer, late flight-commander in the German Air Service, was one of the Prussian irreconcilables, who, rather than submit to the peace terms enforced by the Allies after the defeat of Germany, resolved to become an aerial brigand, an outlaw of the nations, and to wage a bitter warfare of violence and plunder against his late enemies.

His proud spirit refused to bend before the conquerors, for the iron shaft of defeat had embittered his soul, particularly against Britain, whom he had ever regarded as the evil genius of the Entente.

One day, when his plans were well matured, he unburdened his spirit to a couple of his friends, kindred souls, men after his own heart, both of them apt pupils of the great Richthofen, who was still referred to by his disciples as "the red airman." They had been engaged that day in dismantling an aerodrome on the edge of the Schwarzwald; to them, at least, a hateful job.

"Comrades," he said, "this peace has ruined us. _Germania delenda est_, but I will not sit still amid the ruins of the Fatherland. Glorious we have lived, like kings of the air; let us not inglorious die."

"I am with you, Rittmeister. I will follow you to the gulfs," exclaimed one of his companions, named Carl, who had been a famous scout pilot in the Richthofen "circus," and the lightning flashed from the young airman’s eyes as he spoke.

"But what can we do against the empires of the world?" asked a Gotha pilot who had raided the English towns a score of times.

For answer the chief turned a withering look upon the last speaker and said:--

"Max, you have faced death a hundred times in the air, and over the British lines. You have thirty enemy machines to your credit, and yet you ask me what can we do?"

"What of it, Rittmeister? Tell us what is in your mind."

"Listen, then, both of you, and I will tell you what still remains for brave men to do. All is not lost while courage and hope remain," and whilst he spoke the German chief drew his two friends away from the half-dismantled aerodrome on the southern edge of the Schwarzwald, to a narrow path that led amongst the trees.

When the aerodrome was hid from view he began to speak once more, huskily at first, as though restraining some pent up excitement.

"I am in possession of a secret," he said, "which I may not tell even to you unless you first swear to follow me on some great adventure."

They both looked at him, not a little amazed and bewildered, and neither spoke for a moment.

"I have chosen you," continued Spitzer, "because I know you to be men of daring and resource. You are both dissatisfied with the condition of things in the Fatherland. Ach Himmel! This occupation of the sacred German soil by the Britisher, the Frenchman and the American is breaking my heart. I will endure it no longer, but I will strike a blow at the enemy before I die."

As he spoke thus, he almost hissed out the words which he uttered, for his voice had now lost its strange huskiness, while his eyes gleamed like the fierce glittering orbs of the tiger about to make its spring from the hidden jungle. Nor was his present madness without its visible effect upon his two companions, for he had strange powers of magnetic influence, this Prussian Junker.

"Donner and Blitz, but you are right, Rittmeister!" exclaimed Carl, the blood mounting to his temples.

"And you, Max, what say you?" and the chief fixed the Gotha pilot with his eyes.

"Ja! ja!" he assented. "I am with you also."

"But the end of this adventure is death!" continued von Spitzer, speaking now more deliberately. "This much I must tell you in all fairness before I proceed further. However much we achieve--and we shall accomplish not a little--there can be no other ending."

"Bah! we have looked too often into the face of that monster to be afraid," returned the scout.

"You speak truly, Carl," replied the chief. "When your machine went down in flames near Cambrai, you passed so close to me that I stalled my Fokker to let you pass, and I saw the smile upon your lips that day as you looked into the face of death. I never expected to see you alive again, but you were saved for this."

Then, amid the gloom of the dark aisles of the Schwarzwald, these two men swore to follow their chief on this last great adventure, as they had followed him during the darkest days of the war.

"And now I will tell you the secret which I hold, and which at present is known only to two other men," said the Rittmeister, and, sitting down about the gnarled roots of an upturned tree, the two airmen listened to the following story:

"You have heard me sometimes speak of a great mathematician and engineer, by name one Professor Weissmann," began von Spitzer.

"Yes, we have heard of him," replied the others.

"He is the greatest living scientist; moreover, he is a practical engineer, and during the last four years he has devoted his time entirely to designing, constructing and perfecting with his own hands, assisted by one other mechanic, a wonderful aeroplane, compared to which neither the Allies nor the Central Powers have anything to approximate."

"Donnerwetter, but why wasn’t it ready before?" exclaimed Max. "It might have turned the tide of battle in the autumn of 1918."

"It’s no use crying over spilt milk," replied the chief. "It could not be completed before."

"And you say that this wonderful machine is now ready," interposed Max, who had flown every type of machine from a single-seater scout to a heavy bomber, and whose professional curiosity had now been thoroughly awakened by the words of the German ace.

"It is ready, and what is more to the point, it is at my disposal," returned the chief briefly.

"Der Teufel! But where is it?"

"I can lead you to it, for it is less than three miles from where we sit at the present moment."

"Himmel!" exclaimed both the pilots, springing to their feet. "Take us to see it, Rittmeister; we have given you our promise."

"Be calm, my friends; you shall see it to-day. But let me put you on your guard. You must not speak of it aloud, but only in whispers, for the secret of this machine is jealously guarded, and its whereabouts is unknown, save to the professor, his assistant and myself."

"Has it ever been flown?" ventured Max.

"Yes."

"Who was the pilot?"

"I was."

"You, Rittmeister?" exclaimed the amazed airmen.

"Yes."

"And you are satisfied at her performances?" asked Carl, gazing steadfastly into the eyes of his chief.

"More than satisfied. She is the most wonderful and responsive thing I have ever flown. You will say the same when you have seen her, and made a trip or two."

"Phew! take us to see her now; I would give ten years of my life to fly in her," said Max, who was getting almost feverish in his anxiety to see this wonderful thing and to handle her controls; for such is the lure of the air, especially to those who have climbed into the azure and sailed amongst the clouds in the days of their youth.

"You shall fly in her," replied Spitzer.

"When?" asked the eager youth.

"When we start our great adventure," replied the chief.

"And when will that be?"

"To-morrow, if you are willing; all our plans are laid."

"Why to-morrow?" asked the others simultaneously.

"Because delay is dangerous. There is always the danger that this secret, so jealously guarded, and hidden away in the depth of the Black Forest, may be discovered. You know that Germany, under the Peace terms, is forbidden for the present to manufacture aircraft."

"Yes, yes; we know it only too well."

"Well, even now," continued von Spitzer, "the British Air Police have got wind of the thing, and their agents are in a dozen different parts of Germany trying to fathom the mystery of this phantom aeroplane, but so far they have not succeeded. All the same, it is time for us to get away, and that is why I have confided my plans to you to-day. Do you wish to withdraw?" and there was just a faint suspicion of a sneer in the tone of the speaker’s voice, as he said this.

"Withdraw? Ach Himmel, no, a thousand times no! I am ready to start to-day," flashed back the ruffled Carl as he replied.

"Gut!" grunted von Spitzer. "Then you shall see this wonderful thing to-night at sunset; I dare not take you there before, and to-morrow, ach! to-morrow, this great adventure will begin."

*CHAPTER II*

*THE WONDER ’PLANE*

The sun was sinking amongst the pines of the Schwarzwald when the three airmen, after traversing for several miles the wild unbroken solitudes of that primeval forest, emerged at length from the dark shadows of the trees on to a little open glade, a natural clearing about two hundred metres in diameter.

"Here we are at last!" exclaimed the chief.

"Himmel! what a perfect little aerodrome," cried the scout pilot.

"But where is the hangar?" asked the more observant Max.

"Hist! Let us wait for the signal," ordered the Rittmeister, waving his companions back to the fringe of the forest.

"But there is not a soul to be seen anywhere," expostulated Carl. "No one ever comes here."

"We must be careful; there is too much at stake," whispered the flight-commander, and then he gave a long, low whistle, repeated twice.

Scarcely had the last sound died away, like the sad piping tone of the woodland robin, than a similar call came in response from the opposite side of the glade.

"Follow me; the way is clear," said the chief as he strode across the clearing towards the spot whence came the signal. And his companions followed him, silently wondering, for, somehow, they felt that they were treading on enchanted ground, and that some interesting _dénouement_ would shortly take place.

As they neared the edge of the forest once more, a movement amongst the trees attracted their attention, and the next instant a solitary figure emerged from the shadows and greeted them. It was the keen, lynx-eyed professor, the great mathematician and engineer; a man about fifty, dressed in a loose working garb, wearing a battered felt hat above his shock of white, wavy hair.

"You are welcome, children of the Fatherland," he said, extending his hand, and fixing the two strangers with his piercing eyes, after this brief salutation.

"I hope we are not late," began von Spitzer, when the first salutation was over and he had introduced his companions.

"The sun is amongst the pines and the shadows of the Schwarzwald deepen," replied the professor, speaking in the language of the forest. "It was the time arranged, but"--and here he paused for a second--"there is no time for delay," and an uneasy look spread over his face.

"You don’t mean that----" began the chief, but the genius forestalled him by adding:--

"Yes, strangers have crossed the clearing to-day. For the first time since I came here, I heard strange voices amongst the trees."

"But they found nothing?"

"Nothing!" ejaculated the professor.

"Good! Then my friends may view the aeroplane," said Spitzer.

"Certainly; let them follow me," and through an opening barely fifteen feet wide, the professor led the way to a combined hangar and workshop, carefully camouflaged and hidden away amongst the trees.

The next instant the two young airmen received the greatest surprise of their lives.

"Der _Skorpion_!" announced the professor.

"Donnerwetter!" came the involuntary cry from both the strangers as their eyes fell upon a new type of aeroplane, with an angry, waspish look about it, that the Bristol Fighter used to wear during the later days of the Great War. Yet it was not a Bristol Fighter by any means, for it was twin-engined, and steel-built throughout, with a central conning-tower, tapering off to a sharp point to improve the stream-line, and a closed-in be-cabined fuselage into which four or six persons might with ease be stowed away.

"But her engines!" exclaimed Max. "How small they are."

"But how powerful!" replied Spitzer. "Each one develops anything up to 400 horsepower."

"Is it possible?" asked Carl, who was already carefully examining the starboard engine, in its covered in and stream-lined casement.

"The propellers are different, too; they’re something like the Fokker’s, but shorter, and they have a peculiar twist, which I have never seen before. What is that for, Rittmeister?" asked the Gotha pilot.

"For vertical climbs, Max," replied the chief, for while the professor stood by, and looked on, interested and amused at the growing enthusiasm for his idol, the Rittmeister, who had been secretly schooled in the hidden mysteries, explained them point by point, for he was a great mechanic and mathematician was this ex-flight-commander.

"Vertical climbs?" echoed the other. "I thought it was impossible."

"Impossible? Rubbish! Nothing is impossible to the man of science. Have you never heard of the Helicopter?"

"You mean that hybrid mongrel the verdammt Yanks and the Britishers have been experimenting with of late, and which has caused so many accidents?"

"The same; only they went the wrong way about it. This propeller, with this driving power behind it, practically gives the vertical ascent, especially when once flying speed has been obtained."

"Blitz, but it is wonderful!" concluded Max, his enthusiasm growing by leaps and bounds, as he continued his examination.

"Why, the propellers are made of steel, and so are the planes," exclaimed Carl, who was now carefully examining the material of which the aeroplane was made.

"Steel, tempered steel, every bit of it--fuselage, propellers, tail fin, rudders. There’s not an ounce of wood about the _Scorpion_," returned the mentor.

"Then the danger of fire is lessened," ventured Max, whose one dread in the air had always been that of fire.

"That danger is eliminated," replied the chief, in a tone of certitude.

"Except by petrol. By the way, where are the petrol tanks?" exclaimed Carl, who had never missed them till now.

"There aren’t any," replied the Rittmeister, smiling. "I was waiting for that question."

"No petrol tanks?" came the astonished cry from both the airmen at once.

"They’re not necessary," returned the other; "and that’s the greatest mystery of all."

"Himmel! Am I dreaming?" exclaimed Max.

"No, you’re wide awake. Don’t stare like that, man!"

"Der Teufel, but how is she driven?" demanded the scout, staring with wide-open eyes from Spitzer to the professor, and from the latter to his mechanic, who had stood by all this while, with arms akimbo, silently amused at the bewilderment of the two strangers.

"Listen," began the Rittmeister. "I cannot explain everything now--time will not permit--but you shall learn all these things before many days are over."

"Yes, go on!"

"The professor has spent years on this series of inventions, both in the workshop and the laboratory, and each discovery has been co-ordinated and fitted into the scheme. The greatest of all his discoveries is the fact that he has been able to discover and to harness an unknown force to drive the motors of the _Scorpion_."

"A highly compressed gas, I suppose," interposed Max, who had taken a science degree at Bonn.

"Certainly, it is a _most_ highly compressed gas, extracted at great pains and labour from the elements. The formulæ for this wonderful new element exist only in the still more wonderful brain of the professor. It has not been committed to paper even, in its final terms and ratios, so that, even should this machine be captured, which it certainly shall not be whilst I am its pilot, it could not be used, once the present supply of this Uranis, as we will call it, is used up."

"That is why the engines are so small, then?" ventured Max.

"Precisely!"

"And what is our present supply of this wonderful element?"

"Do you see this?" said the Rittmeister, pointing to a few small cylinders, each about two feet long, and six inches in diameter, which lay carefully piled upon each other on the floor near the _Scorpion_.

"Yes."

"That is the world’s supply at present, excluding the two cylinders which are already fitted on the machine."

"The world’s supply," ejaculated Carl, who was thinking of the huge petrol tank, which in a Fokker scout would last only three hours with the throttle wide open. "That won’t last long, unless the pressure is enormous."

"The pressure is enormous, my friend; so enormous that if anything happened it would----"

"Blow a hole in the universe, I reckon," interposed Max.

"You are right, and that is the only danger connected with the _Scorpion_. The other danger you mentioned, that of fire, is altogether eliminated. There would be nothing to burn if one of these cylinders exploded, for there would be nothing left--in the vicinity."

"_Sacre bleu_!" exclaimed Carl, _sotto voce_, for, brave youth that he was, he shuddered at the thought.

Max was the more practical of the two, however, for he belonged not to the highly sensitive scouts, but to the heavy bombers, and he merely asked to satisfy his curiosity:--

"How far will one of those cylinders take us, Rittmeister?"

"Ten thousand miles," replied the chief, "that is, one fitted to either engine."

"Good! Let me see, there are ten here, and one already fitted to either motor makes a dozen. Why, they would carry us"--and here he made a rapid calculation--"they would take us twice round the world."

"Precisely, and with a little to spare, when we had completed the double trip."

"And what speed would she pick up, say at a level flight?"

For answer the chief looked at the professor, as though uncertain whether to reply to this question.

"They have taken the oath, sir," he pleaded, "They cannot withdraw," and the great scientist nodded his acquiescence.

"Two hundred and fifty miles without being pushed," he replied at length.

"Donnerwetter! And what if she were pushed?"

"I cannot say, she has never been driven beyond that."

"What a deuce of a noise she will make--like a whole formation of Gothas, I should imagine," said Max.

The professor smiled, but left it to the Rittmeister to explain this last point.

"The engines are silent, but there is a slight hum from the propellers. That cannot be effaced at present, but it is nothing."

Then, having given all these details, the visitors made a closer inspection of the machine. They were permitted to climb into the conning-tower, to handle the controls, and the two swivel machine guns mounted there. They were shown into the little cabin, where four men might sit at the little table, or lie down at full length, but could not stand upright. The steel struts, steel folding wings, the carefully packed spares, the little mica windows in the cabin--these, and a dozen other things, were pointed out and explained to them--the stores which were already packed, comprising chronometrical instruments, maps, charts, ammunition for the guns, compressed food, etc., until their bewilderment grew, and their astonishment became unbounded.

"Why, she scarcely needs an aerodrome at all!" Carl ventured at length.

"Scarcely," replied the chief. "At any rate, not for a long time."

"She is weather proof; she is wonderfully camouflaged. She could hide in a desert, or a meadow," said Max.

"And she carries her own stores for a long, long trip," ventured Carl, who was just dying for the morrow to come.

"And if she were chased, she could make rings round anything, even a Fokker scout, or a verdammt British S.E.5," added Max.

"So you are satisfied, both of you?" asked the Rittmeister.

"Perfectly satisfied. I am only longing for to-morrow, so that I may turn aerial brigand, buccaneer, or what you like," answered Carl.

"And you, Max?"

"I am ready, chief, to follow you to the end of the world, for mine eyes have seen the wonder ’plane."

*CHAPTER III*

*"TEMPEST" OF THE AERIAL POLICE*

Colonel John Tempest, D.S.O., M.C., etc., late of the Royal Air Force, and now Chief Commissioner of the British Aerial Police, sat before a pile of papers in his office at Scotland Yard late one evening. He was anxious and worried, for something had gone seriously wrong with his plans.

It was his duty to investigate and track down all aerial criminals, whether brigands, smugglers or revolutionists of the Bolshevist type. For this purpose he had been appointed by the Government to the command of the British Aerial Police, whose functions included the patrolling of the routes of the great aerial liners throughout the British Isles, and the All-Red route to Egypt, India, and other British possessions, and the careful guarding and watching of the aerial gateways and ports.

Some of the best scout pilots of the war, including two famous secret service men, named Keane and Sharpe, were detailed to assist him in this important and ever-increasing task, for aerial crime of twenty different kinds was becoming more and more prevalent since the war.

So far his efforts had been conspicuously successful, and he had brought many of the offenders to justice, but at the present moment he had to confess himself baffled--utterly baffled by a series of unfortunate occurrences which it had been beyond his power to prevent.

"There is some master-mind behind all this," he exclaimed to himself, rising suddenly from his chair, and beginning to pace the room, much in the same way that he used to pace his squadron office, in the old days, when, as commander of a squadron of scouts during the Great War, he had attempted to outwit the daring of the German airmen.

"I wonder now--I wonder what happened to that missing German professor!" and Colonel Tempest suddenly halted, and placed his left hand to his forehead, as some powerful, new idea had arrested his mental faculties.

Then, walking across the room swiftly, he switched on a shaded light which illuminated a large map of Germany, showing the aerial routes, the lines of occupation by the Allies, etc.

"It is just possible," he murmured to himself, "that the two things are connected--the disappearance of this eminent scientist and the appearance of this extraordinary flying machine." Then he switched off the light, and returned to the sheaf of papers and documents on his desk. He sorted out one and placed it on top; it was a decoded message, received some days ago from one of his agents at Constantinople. It ran as follows:--

"Mysterious aeroplane, phantom-like in appearance, passed over here yesterday flying at terrific speed. All our signals disregarded. No navigation lights showing. Our fast scouts gave chase but left hopelessly behind. Came from direction of Adrianople, crossed the Bosphorus, and disappeared rapidly flying south-east. Time shortly after sunset.

AERIAL, CONSTANTINOPLE."

"That is three days ago," continued the Colonel, still thinking aloud, "and here are four similar messages from other sources showing quite plainly the route taken. Great Heavens! if I were not tied to my desk in this place, I would take the fastest scout in the country and chase this infernal night-wizard myself."

A soft tap at the door startled the Commissioner, for during the last three days he had become highly nervous; this affair was getting on his mind, but he recovered himself instantly and called out in a deep voice:--

"Come in!"

The door opened softly and his confidential secretary entered, and announced:--

"Two more cables and a wireless message, sir."

"Anything from Keane or Sharpe yet?" demanded the chief.

"Nothing, sir."

"Then what are these confounded things?"

"More about that aerial brigand, sir."

"Let me see them," and Jones handed the messages to his chief.

Consternation and alarm were both visible on the face of Tempest as he read the news.

"So the devil has already got to work, Jones," he remarked, quoting from the sheets, laconic phrases such as "Oil tanks at Port Said burning for three days. Crew of mysterious aeroplane suspected." (Delayed in transit.) "Wireless station at Karachi utterly destroyed, after brief visit by strange airmen." The third was a wireless message which proved most disconcerting of all to the Commissioner. It announced that a silent aeroplane, showing no distinctive marks whatever, passed over Delhi "this afternoon" at a speed estimated at not less than three hundred miles an hour.

The chief of the aerial police leaned back in his chair and groaned.

"Three hundred miles an hour!" he gasped; "but the silent aeroplane idea is a fallacy. It is impossible with any type of internal-combustion engine. It must either have been too high up for the good people of Delhi to hear it, or its engines must have been shut off, or well throttled down. Bah! I know too much about aeroplanes to swallow that." Then rounding upon Jones, who was standing by awaiting instructions, he said sharply:--

"Did that second message go out to Keane?"

"Yes, sir."

"And there’s still no reply from him?"

"Nothing whatever, sir."

"H’m. I cannot understand it. Send it out again by wireless telephone; he may be on his way back by aeroplane now, and possibly within reach."

"Right, sir," and Jones disappeared to stab the ether waves again in search of Keane. At that moment the telephone bell on the Commissioner’s desk rang. It was the Home Secretary asking for Colonel Tempest, for the same messages concerning the aerial brigand had reached him.

"Hello, Tempest; is that you?"

"Yes; who is that?"

"Lord Hamilton, speaking from the Home Office."

"Oh, yes, my lord."

"I say, Tempest, what is this news just to hand about aerial highwaymen romping half round the British empire, destroying wireless stations, and burning out the big oil tanks along the All-Red Route? I thought you had all these aerial criminals well in hand. There’ll be a deuce of a row about all this when Parliament meets in two days’ time."

"Well, er--we’re doing our best to deal with it, sir, but it will take time to lay these fellows by the heel, I fear."

"Have you got the matter in hand?"

"Yes, sir."

"What have you done? I shall be bombarded with questions shortly; in fact, the Colonial Secretary’s here now. He’s complaining that the routes are not sufficiently well patrolled. What steps have you taken to deal with these marauders?"

"I’ve wirelessed to all the aerial stations, to get their fastest scouts out all along the line at once to look for these bandits, and I’m staying on here all night expecting news every moment."

"Very well. Keep me informed of everything that happens. It’s becoming very serious. You have full powers to deal effectively with these criminals, and they may be shot down at sight if they don’t respond to signals."

Then, as the angry minister rang off, another tap was heard at the door, and the imperturbable Jones entered once more, and announced:

"Message from Keane and Sharpe came in whilst you were speaking on the telephone, sir."

"Good!" ejaculated Tempest, as he wiped the perspiration from his brow, for he had expected something much worse from the Home Secretary. "What does the message say?"

"They received my last message, sir, and are on their way home by the fastest aeroplane. They are due at Hounslow aerodrome at midnight."

"Excellent! What time is it now, Jones?"

"It wants ten minutes to midnight, sir, and I have sent out the fastest car to meet them and bring them straight here. They should be here in half an hour, sir."

"Have you told them at Hounslow?"

"Yes, sir, and they have already got out the coloured lights and the ground flares."

"You have done well, Jones, but you had better not leave the office to-night. I’m very sorry, but I may want you. This is urgent business; we’re up against something this time, and unless Keane and Sharpe have found something out, we’re going to be beaten."

"I’ll stay, sir, but what about you? This is your third night-sitting, and you’ve had nothing since lunch. Shall I order supper for you?"

"Oh, thanks, Jones, but I’d forgotten. Yes, you may order me coffee and a sandwich, and get something for yourself. You’re getting the strain as well, and I don’t want you to break down."

When left alone, Colonel Tempest once more began to pace the soft-carpeted room, much as a captain paces the bridge when his thoughts are unduly disturbed by some untoward event during the watch of the second officer. Every other minute he consulted his watch, and wondered why the time passed so slowly. Twice he rang down to the lobby attendant and asked if Captain Keane had arrived, and twice the same answer was returned.

Then he looked at the maps on the wall, and followed with his finger the trail of the All-Red Route which the aerial liners followed, linking up the empire and half the world. Now and again he would glance shrewdly at the large map of Germany, as a skipper eyes the weather quarter when a storm is brewing. Occasionally he would murmur half aloud:--

"A silent engine ... three hundred miles an hour. Gee whiz! but they have beaten us two to one. We shall never catch them."

Then a slight sound caught his ears from outside the great building. The soft purr of an approaching Rolls-Royce motor and the sharp blast of a Klaxon horn followed.

"At last!" he cried. "Here they come!"

*CHAPTER IV*

*A MIDNIGHT CONSULTATION*

The next moment the door burst open and two men in flying helmets and leathern coats entered the room, and saluted the Colonel. Without any ceremony the latter greeted them warmly, almost joyously, for their cheerful presence gave almost instant relief to his over-burdened mind.

"Good evening, Keane. Good evening, Sharpe," he exclaimed, stepping forward and gripping each of them warmly by the hand.

"Good evening, sir."

"Now, have you discovered anything?" began the chief, without waiting for them to divest themselves of their heavy gear.

Keane looked at the Commissioner for a second or two and then answered:--

"Yes, and no, Colonel."

"H’m. That means something and nothing, I presume."

"Exactly, sir," continued Keane, who acted the part of spokesman. Then, speaking more solemnly, and in lowered tones, he continued, "We are up against something abnormal; I had almost said something supernatural. When you recalled us we were hot on the trail of the man who, in my opinion, is behind this conspiracy."

"You mean this Professor Weissmann?" added the chief of the aerial police.

Keane nodded.

"I thought so. This man is evidently an evil genius of very high mental calibre, and he has determined, out of personal revenge for the defeat of Germany, to thwart the Allies, and in particular Great Britain."

"He is a master-mind, and a highly dangerous personality; dangerous because he is so clever. And now that he has secured a few daring airmen for his tools, there is no end to the possibilities which his evil genius may accomplish before he and his crew are run to earth," replied Captain Keane.

"I know it, I know it--look here!" and the colonel handed him the batch of cables and wireless messages which showed how the _Scorpion_ had already got to work.

"H’m! and there will be worse to follow," added the airman after he had glanced through the list.

"Now, tell me briefly what you have found, Keane, after which we must get to work to devise some immediate plan to thwart these aerial brigands. But first take off your flying gear, and sit by the fire, for you must be hungry, tired and numbed after that cold night ride." Then, ringing for his attendant, he ordered up more strong coffee and sandwiches.

"Thanks, Colonel, I will not refuse. It was indeed a cold ride, and we had no time to get refreshments before leaving the aerodrome at Cologne this evening," said Sharpe, as he divested himself of his heavy gear, sat by the fire and enjoyed the coffee which soon arrived.

A few moments later, the three men were engaged in serious conversation, although the hour of midnight had long since been tolled out by Big Ben.

"You sent me," Keane was saying, "to discover the whereabouts of this great German engineer and man of science, this brain wave whose perverted genius is likely to cost us so dear."

"And you were unable to find any trace of him?" interposed the chief.

"Well, we were unable to come into contact with him, for we found that since peace was concluded he had vacated his professorial chair at Heidelberg University, where he had been engaged for some considerable time, not only on some mechanical production, but in an attempt to discover some unknown force, evidently a new kind of highly compressed gas to be used for propulsive purposes."

"Had he been successful?"

"That, it was impossible to find out during our short stay over there," replied Keane, "but I discovered from someone who had been in close touch with him just about the time peace was signed, that he had expressed himself in very hopeful terms."

"Was he a very communicative type of man, then, did you learn?"

"No; on the contrary, he seldom spoke of his work, but on this occasion, when he communicated this information, he was very much annoyed at the defeat of Germany, and considered that his country had been betrayed into a hasty peace."

"And what happened to him after that?" asked the colonel.

"Shortly afterwards he disappeared completely, taking with him all the apparatus connected with his research work, also a highly skilled mechanic who had been specially trained by him for a number of years. But he left not a trace of himself or his work," said the captain, pausing for a moment to light a cigarette.

"Do you think he is acting under any instructions from his authorities?"

"No, certainly not; he distrusts his present Government entirely, and considers them traitors to the Fatherland."

There was another brief silence, whilst the three men, wrapt in deep thought, sat looking into the fire, or watched the rings of tobacco smoke curling upwards to the ceiling. At last, Captain Sharpe observed:--

"A powerful intellect like that did not suddenly disappear in this way without some ulterior motive, Colonel Tempest."

"Obviously not," returned the latter briefly, for he was deep in contemplation, and his mind was searching for some clue. At length he turned to the senior captain and said:--

"This silent engine theory, Keane, what do you think of it?"

Keane shook his head doubtfully, and the colonel handed to him once more the recent wireless message from Delhi, adding merely:--

"Do you think it possible?"

"Scarcely," replied Keane carefully, "but with a master mind like this, one never knows. It will be necessary for you to consult the most eminent professors of science and chemistry at once."

"I intend to visit Professor Verne at his house first thing to-morrow, or rather to-day, for it is already morning."

"But the aeroplane," added Sharpe, who had been perusing the Delhi message, "this also must have been specially built for this new gas."

"Given the one, the other would naturally follow, and would be the lesser task of the two, for this man is a great engineer as well," said Keane.

"It is a deep well of mystery," continued Tempest after another pause; "but something must be done at once. To-morrow the morning papers will be full of it. Next day Parliament meets, and questions will be asked, and it will all come upon us. I shall have to meet the Home Secretary as soon as I have interviewed Professor Verne, and Lord Hamilton will not be easily satisfied. The public will also be clamouring for information on the subject, and they will have to be appeased and calmed. The Stock Exchange will begin to talk also, and to demand compensation for the companies whose properties have been damaged. Insurance rates, marine and otherwise, will be raised, and Lloyd’s underwriters will not fail to make a fuss. Now, gentlemen, what steps can we take to deal with these raiders in the immediate future?"

Send us after this mystery ’plane on fast scouts with plenty of machine-gun ammunition," urged Sharpe.

"I cannot spare you for that, but I have already ordered strong patrols of aerial police to search for the brigands. I must have you here or somewhere within call. At any rate, I cannot let you go further than Germany. It may be necessary to send you there again."

"On what account, sir?" asked Keane.

"To find the aerodrome which this raider calls ’home,’ for he must have a rendezvous somewhere if only to obtain supplies and repairs."

"And that secret aerodrome must be somewhere in Germany, hidden away in some out-of-the-way place," ventured Sharpe.

"But in what part of Germany?" asked the commissioner.

"Let me see," cried Keane, rising to his feet, and walking across the room to where the large map of Germany hung upon the wall--"why, it must be in the Schwarzwald!"

"The Schwarzwald!" exclaimed the other two.

"Yes, it is by far the best hiding-place in the whole country. One may tramp for days and never see a soul. It must be somewhere in the Schwarzwald."

"Then to the Schwarzwald you must go to-morrow, adopting whatever disguises you desire, and you must find this hidden spot where the conspiracy has been hatched," concluded the colonel.

*CHAPTER V*

*THE AERIAL LINER*

The airship liner, _Empress of India_, was preparing to leave her moorings, just outside the ancient city of Delhi, for Cairo and London. This mammoth airship was one of the finest vessels which sailed regularly from London, east and west, girdling the world, and linking up the British Empire along the All-Red Route. She had few passengers, as she carried an unusually heavy cargo of mails for Egypt and England, and a considerable amount of specie for the Bank of England. Several persons of note, however, figured amongst her saloon passengers, including the Maharajah of Bangapore, an Anglo-Indian judge, and a retired colonel of the Indian army.

She was timed to depart at mid-day, and during the morning mailplanes had been arriving from every part of India with their cargoes of mail-bags, already sorted for the western trip.

The great mammoth now rode easily with the wind, moored by three stout cables to the great tower which rose above the roof gardens of the air-station. An electric lift conveyed the passengers and mails to the summit of this lofty tower, from whence a covered-in gangway led to the long corridors which lined the interior of the rigid airship.

"Have all the engines been tested?" the captain asks of the chief engineer, as he comes aboard with his navigating officer.

"Yes, sir."

"All the passengers aboard?" he asks next of the ground officer.

"All except the maharajah, Captain, and I expect him any moment."

"Excellent," replied the skipper. "There’s a good deal of bullion aboard from the Indian banks, I hear, and the rajah himself is likely touring a lot of valuables with him, I understand, as he is to attend several court functions at St. James’s Palace."

"Yes, sir. I hope you won’t meet that aerial raider," replied the ground officer.

"Poof! What can he do? He can’t board us in mid-air! Besides, I hear that the aerial police are on his track, and that all their fast scouts are patrolling the mail routes."

"Yes, you’ll have an aerial escort with you for the first two hundred miles, Captain. They’ll pick you up shortly after you leave here."

"Absolutely a waste of time. The police could be much better employed in searching for these rascals."

"Well, perhaps you’re right," replied the ground official. "They certainly cannot board you in mid-air, as you observe, and they cannot set you on fire as they did the early Zeppelins, for helium won’t burn."

This conversation was interrupted by shouts and cheers which reached the speakers from down below.

"Hullo! here comes the rajah. I must go down and welcome him," said the captain, as a fanfare of trumpets announced the arrival of the great Indian chief.

Then, with all the ceremonial and pomp of the East, the Maharajah of Bangapore was welcomed aboard the luxurious air-liner, and, accompanied by his personal attendants, he was shown with much obsequiousness to his private saloon. His baggage, containing treasures worth a king’s ransom, was likewise transferred, under the supervision of his chamberlain, from the ground to his suite of apartments.

The clock in the palace of the Great Mogul in the old city of Delhi strikes twelve, and the captain’s voice is heard once more, as he speaks from the rear gondola:--

"All ready?"

"Yes, sir, all clear!"

A button is pressed and the water ballast tanks discharge their cargo to lighten the ship, and then swiftly comes the final order:--

"Let go!"

And as the cables are slipped from the mooring tower, the light gangway is drawn back, the crowd down below cheer, and the giant airship backs out, carried by the force of the wind alone till she is well clear of the station. Then her engines open up gradually. She turns until her nose points almost due west, then slips away on her four thousand miles’ journey over many a classic land, desert, forest and sea towards the centre of the world’s greatest empire.

About four o’clock that afternoon, as Judge Jefferson sat and talked with his friend Colonel Wilson in one of the rear gondolas where smoking was permitted, he remarked that this was his seventh trip home to England by the aerial route, and declared that he could well spend the rest of his lifetime in such a pleasant mode of travel.

"There’s no fatigue whatever," he added; "nothing of the jolt and jar which you get in the railway carriage. As for the journey by sea, I was so ill during my last voyage that I simply couldn’t face the sea again. A storm at sea is of all things the most uncomfortable. If we meet with a storm on the air-route we can either go above it or pass on one side, as most storms are only local affairs."

"Not to speak of the time that is wasted by land or sea-travel," added the colonel.

"Exactly," replied the judge.

"Only to think that in forty-eight hours we shall be in London, even allowing for a two hours’ stay in Cairo to pick up further mails and passengers."

"Wonderful! Wonderful!" agreed his companion.

"And the absence of heat is some consideration, when travelling in a land like India," continued the colonel as he flicked off the end of his cigar.

"Yes. The stifling heat, particularly in May, June and July, when you get the hot dry winds, is altogether insufferable in those stuffy railway carriages, while up here it is delightfully cool and bracing, and the view is magnificent."

"Hullo! what is that fine river down there?" asked the judge, as he looked down through the clear, tropical atmosphere on to the delightful landscape of river, plain and forest three thousand feet below.

"Oh, that must be the Indus, the King River of Vedic poetry, a wonderful stream, two thousand miles in length," said the colonel, consulting his pocket map.

"Can it really be the Indus?"

"It is indeed."

"Then we have already travelled four hundred miles since noon across the burning plains of India, and we have reached the confines of this wonderful land," replied Jefferson.

"Yes, we have indeed. We shall soon enter the native state of Baluchistan. See yonder, right ahead of us, I can already make out the highest peaks of the Sulaiman Mountains. We are already rising to cross them."

"And this evening we shall cross the troubled territory of Afghanistan."

"Yes," replied the colonel, "and by midnight, if all goes well, we shall be sailing over Persia."

"Persia, the land of enchantment," mused the judge.

"And of the _Arabian Nights_, those wonderful tales which charmed our boyhood--the land of Aladdin, of the wonderful lamp, and the magic carpet."

"The magic carpet," laughed the judge. "This is the real magic carpet. The author of that wonderful story never dreamt that the day would really come when the traveller from other lands, reclining in luxury, would be carried through the air across his native land, by day or by night, at twice the flight of a bird."

And so these two men talked about these wonderful classic lands over which they were sailing so serenely, of Zoroaster, the great Persian teacher of other days, of Ahura Mazda, the All-Wise, and the Cobbler of Baghdad, until the tea-bell startled them.

Then, finding they were hungry because the bracing air had made them so, they passed on to the snug little tea-room, where, amid the palm-trees and the orchids, they listened to soft dulcet notes from a small Indian orchestra which accompanied the maharajah. Here, they sipped delicious china tea from dainty Persian cups, and appeased their hunger, as best they could, from the tiny portions of alluring _patisserie_ which usually accompany afternoon tea.

But, later that evening, they did ample justice to a fuller and nobler banquet, which had been prepared for them in the gilded and lofty dining saloon; for they were the honoured guests of the Maharajah of Bangapore. And he entertained them right royally as befitted one of his princely rank.

And in all the wondrous folk-lore and tradition of the ancient Persian kings, was there ever a more regal banquet, or one more conspicuous by the splendour of its oriental wealth than this long-protracted feast? Rich emblazoned goblets of gold, bejewelled with rare and precious gems, adorned the table, for the prince had brought his household treasures; they were to him his household gods, and heirlooms of priceless worth.

Never the Lydian flute played sweeter music than these soft native airs which wandered amid the eastern skies, as, under the silver moon, the long, glistening, pearl-like airship sailed on beneath the stars, while down, far down below, lay the ruins of Persepolis, where the ancient kings of Persia slept their last long sleep.

*CHAPTER VI*

*AN UP-TO-DATE CABIN BOY*

While the great, mammoth air-liner is racing like a meteor across the eastern skies, on its way to Cairo and London, it is necessary to introduce to the reader a chirpy, little fellow called Gadget. In fact, this cute little chap, who stood a matter of four feet two inches in his stockinged feet, deserves a chapter or two all to himself.

Now Gadget did not belong to the passengers, nor did his name appear at all in that distinguished list. Neither did he rightly belong to the crew, except in the matter of his own opinion--on which subject he held very pronounced views. But he certainly did belong to the airship, and appeared to be part of the apparatus, or maybe the fixtures and effects. He certainly knew the run of that great liner, every nook and corner of it, better even than the purser or the navigating officer.

To tell the truth, this insignificant but perky little bit of humanity was a stowaway, who had determined, at twelve years of age, to see the world, at the expense of somebody else. How he came aboard, and hid himself amongst the mail-bags, until the airship had sailed a thousand miles over land and sea, still remains a mystery. But it happened that, when the _Empress of India_ was crossing the blue waters of the Adriatic sea, on her outward voyage, there came a tap at the captain’s door one afternoon when the latter had just retired for a brief spell.

"Come in!" called the air-skipper, in rather surly tones, wondering what had happened to occasion this interruption.

The next instant, the chief officer entered the little state-room, leading by a bit of string, attached to one of his nether garments, the most tattered-looking, diminutive, but perky little street Arab the captain had ever beheld.

"What in the name of goodness have you got there, Crabtree?" exclaimed the skipper, starting up from his comfortable bunk, at this apparition.

"Stowaway, sir!" replied the officer briefly.

"Stowaway?" echoed the captain.

"Yes, sir."

"Where did you find him?"

"Didn’t find him, sir. He gave himself up just now. Says he’s been hiding amongst the mail-bags. What shall I do with him, sir?"

"Tie him to a parachute and drop him overboard as soon as we are over the land again," shouted the captain in angry tones. "I won’t have any stowaways aboard my ship."

This was said more to frighten the little imp than with real intent, though the air-skipper spoke in angry tones, as if he meant what he said. He was evidently very much annoyed at this discovery.

"He’s half-frozen, sir," interposed the chief officer in more kindly tones.

"Humph! Of course he is," added the captain. "This keen, biting wind at three thousand feet above the sea must have turned his marrow cold. Besides, he hasn’t enough clothes to cover a rabbit decently. Just look at him!"

The little chap’s eyes sparkled, and his face flushed a little at this reference to his scant wardrobe. But he knew by the changed tone in the captain’s voice that the worst was now over. He had not even heard a reference to the proverbial rope’s-end, a vision which he had always associated in his mind with stowaways.

"My word, he’s a plucky little urchin, Crabtree!" declared the air-skipper at length, his anger settling down, and his admiration for the adventurous little gamin asserting itself as he gazed at the ragged but sharp-eyed little fellow.

"What is your name, Sonny?" he asked at length.

"Gadget, sir," whipped out the stowaway.

"Good enough!" returned the captain smiling. "We’ve plenty of gadgets aboard the airship, and I guess another won’t make much difference. What do you say, Crabtree?"

"Oh, we’ll find something for him to do, sir. And we’ll make him earn his keep. He’s an intelligent little shrimp, anyhow."

"How old are you, Gadget?" asked the captain.

"Twelve, sir!" replied the gamin.

"Father and mother dead, I suppose?"

"Yes, sir."

"Been left to look after yourself, Gadget, I reckon, haven’t you?" said the skipper kindly, as he gave one more searching glance at the small urchin, and noted how the little blue lips quivered, despite the brave young heart behind them.

There was no reply this time, for even the poor, ill-treated lad could not bring himself to speak of his up-bringing.

"Never mind, Gadget...!" interposed the skipper, changing the subject. "So you determined to see the world, did you, my boy?"

"Yessir!" came the reply, and again the sharp eyes twinkled.

"Well, you shall go round the world with me, if you are a good boy. But, if you don’t behave, mark my words"--and here the captain raised his voice as if in anger--"I’ll drop you overboard by parachute, and leave you behind! Do you understand?"

The urchin promised to behave himself, and, in language redolent of Whitechapel, began to thank the captain effusively.

"There, that will do! Take him away, and get him a proper rig-out, Crabtree," said the skipper impatiently. "I never saw such a tatterdemalion in all my life."

"Come along, now, Gadget," ordered the chief officer, giving a little tug at the frayed rope, which he had been holding all this while, and, which, in some unaccountable way, seemed to hold the urchin’s wardrobe together.

This little tug, however, had dire results, in-so-far as the above mentioned wardrobe was concerned. It immediately became obvious that it not only served as braces to the little gamin, but also as a girdle, which kept in a sort of suspended animation Gadget’s circulating library and commissariat. For, even as the janitor and his prisoner turned, the rope became undone, and, though Gadget by a rapid movement retained the nether part of his tattered apparel in position, yet his library--which consisted of a dirty, grease-stained, much worn volume--and his commissariat--composed of sundry fragments of dry crusts of bread wrapped in half a newspaper--immediately became dislodged by the movement, and showered themselves in a dozen fragments at the captain’s feet.

"Snakes alive! what have we here?" demanded that august person, as he stooped and picked up the book. Then he laughed outright, as he read aloud from the grubby, much-thumbed title page:--

_Five weeks in a Balloon_ ... by Jules Verne.

The mate grinned too. He remembered how that same book had thrilled him, not so long ago either. And, perhaps, after all, it was the same with Captain Rogers.

"Where did you get this, Gadget?" asked the captain, reopening the conversation, after this little accident.

"Bought it of Jimmy Dale, sir," replied the boy readily.

"And how much did you pay for it?"

"Gev ’im my braces, an’ a piece o’ tar band for it, sir."

The captain ceased to laugh, and looked at the boy’s earnest face. And something suspiciously like a tear glistened in the eyes of the airman, as he replied:--

"You actually gave away to another urchin an important part of your scanty wardrobe to get possession of this book?"

"Oh, it wur a fair bargen, sir. Jimmy found the book on a dust heap, but I wasn’t takin’ it fur nothin’. And then Jimmy never had any braces."

"I see. Very well, you can go now, Gadget. Mr. Crabtree will find you some better clothes, and get you some food. Then you shall report to me to-morrow. See, here is your treasured book," said the skipper, dismissing the urchin once more.

"Thank you, sir," returned the boy, pulling a lock of unkempt hair which hung over his forehead, by way of salute. "I’ll lend you the book, sir, if you’ll take care of it," and the chief officer smiled as he led the little chap away.

So that was how Gadget became part of the fixtures and apparatus of the air liner. He was more than an adventurer, was Gadget. He might even have been an inventor or a discoverer, if he had met with better fortune in the choice of his parents. His sharp, young brain was full of great ideas.

In less than a couple of days, rigged out in a smart pair of overalls, which had been very considerably cut down, he was soon perfectly at home aboard the great liner. But then he was so adaptable. As an up-to-date cabin boy, the captain declared that he never knew his equal.

He became a general favourite, and in a very short space of time he discovered more about airships and internal-combustion engines than many a man would have learnt in six months.

It was no use, therefore, to argue with the boy that he didn’t belong to the crew of the _Empress_. And it just wasn’t worth while to inform him that, as he was still of school age, he would be handed over to the authorities, or placed in a reformatory, as soon as the vessel returned to England. Gadget had made up his mind that he wouldn’t. In a little while it even became an open question whether Gadget belonged to the airship or the airship belonged to Gadget.

"I hain’t argefyin’ with you, I’m telling ye. This is the way it should be done!" he was heard to remark to one of the air mechanics one day, after he had been on the vessel about a week. The point at issue concerned a piece of work on which the mechanic was engaged, and Gadget had even dared to express his point of view. The extraordinary thing was that Gadget was right.

Ships and railway engines were all right in their way, but they were not good enough for Gadget. Aeroplanes and airships were much more to his liking. He was thoroughly alive and up-to-date, and though some months ago, when this fever of world travel first seized upon him, he had more than once considered the question of stowing himself quietly away on some outward bound vessel from the West India Docks in London, his fortunate discovery, and ultimate possession of that tattered copy of _Five Weeks in a Balloon_, had caused him to change his views.

Ever since reading that volume he had had no rest. Even his dreams had been mainly concerning balloons and their modern equivalents, airships.

"I will see the world from an airship," he had confidently announced to himself one day. "I will sail over tropical forests and lagoons, over deserts and jungles."

This had been his dream and his prayer. But unlike many older folk, Gadget had left no stone unturned in order to answer his own prayer. He had carefully followed the newspapers (for he had earned many a shilling by selling them) for the movements of the new air liner and the opening up of the All-Red Route. And when the time had arrived for the airship to sail, watching his opportunity the little fellow had smuggled himself on board, and here he was, having now almost sailed around the world, crossing the Arabian desert on the homeward voyage.

*CHAPTER VII*

*A DUEL WITH WORDS*

Gadget’s activities, however, were not confined merely to the duties of cabin boy, although his diminutive size and his rapidity of movement made him very useful in that capacity. To fetch and carry for the skipper or chief officer along that 670 feet of keel corridor was to him a life of sparkle and animation. But, when no particular duty called him, the pulsating mechanism of that mighty leviathan irresistibly attracted him.

His round, closely cropped, well shaped head, and his roguish little face, would suddenly appear in the wireless cabin or in one of the four gondolas, where the powerful Sunbeam-Maori engines drove the whirling propellers.

Ship’s mascot and general favourite though he was, his sharp wits soon enabled him to make himself almost indispensable. At length, however, the everlasting call seemed to be----

"Gadget! Gadget! Where is the little rascal? What mischief is he up to now?"

For it must be admitted that the overwhelming curiosity of the urchin sometimes got him into trouble. In this respect he had particularly fallen foul of Morgan, the third engineer, a short, stout, somewhat stumpy type of Welshman, whose spell of duty generally confined his activities to the care of the twin-engines in the rear gondola.

It appears that Gadget had unwittingly broken the rules and regulations of the airship by smuggling two parcels of tobacco aboard during a brief stay in one of the air ports. He knew full well that a little fortune awaited the man who could unload smuggled tobacco down the Whitechapel Road, and the temptation had been too great for him. He had been discovered, however, and the captain had punished him for the offence.

Now, Gadget was still smarting under this punishment when one day he startled the third engineer by his sudden and unlooked for appearance in the rear gondola.

"How now, you little rascal!" exclaimed Morgan, throwing a greasy rag at the boy. "How much did you make on that tobacco?"

"Stop smokin’ on dooty, will yer, an’ mind yer own bisness!" rasped out the urchin, feeling that both his dignity and importance were being imperilled by this reference to his recent offence.

"Go away!" snarled the bad-tempered Welshman, surreptitiously hiding the still smoking cigarette.

"Yah! Why don’t yer get more ’revs’ out o’ those rear engines?" yapped the insulting little Cockney boy, repeating a few words used by the captain himself the day before, and preparing to beat a hasty retreat through the doorway.

"You dirty ragamuffin!" shouted the stout man, flushing with anger, and hurling the oil can, which he held in his hand, at the gamin.

For one instant the tantalising little street arab disappeared on the other side of the door, but, when the missile had spent its force, and had crumpled up against the panelling, leaving a pool of oil on the floor, the urchin’s head reappeared once more. The opportunity was too good to be lost. All the vivacity of the boy was pitted against the hot tempered Welshman, and Gadget was a master of invective, and had a wonderful command of high sounding words, the real meaning of which, however, he did not properly understand. But he was just dying for another of these encounters, so common in his experience of things down Stepney way, or along the West India Dock Road.

"Call yerself an ingineer?" came the next gibe from the saucy, impudent little face, now distorted into something grotesque and ugly. "We’ll be two hours late at Cairo, an’ all because you ain’t fit to stoke a donkey-ingine."

"Ger-r-r-o-u-t!" shouted the angry man, making a rush for his tormentor. "I’ll break your head if you come in here again!"

"I’d like ter see yer!" came the tart reply, ten seconds later, as the head reappeared once again, for Gadget had retreated swiftly some way down the keel corridor, as his opponent made for him with a huge spanner.

The engineer had determined to lock the door of the little engine-room against the little stinging gad-fly, but of course the sharp-witted rascal had outwitted, or "spike-bozzled" him, as they say in the Air Force, by snatching the key and locking the communication-door on the outer side.

Morgan was beginning to find out to his cost that it was a very unwise proceeding to cross the path of this pertinacious stowaway. He could not get rid of him, and this morning, after the skipper’s recent remarks, he was trying to recover his lost reputation by extra attention to his engines. Besides, the captain would be along on his rounds again soon, and, if the engines were not doing their accustomed revolutions, there might be trouble.

Thinking he had now got rid of his tormentor, Morgan turned to examine his engines, when the key turned softly in the lock once more, and the irrepressible mascot, peering through the slightly open door, grinned, and then gave vent to the one word, which means so much:--

"Spike-bozzled! Yah!"

"You’re a little villain!" roared the engineer.

"You’re an incubus!" retorted Gadget.

"Go away!"

"Swollen head, that’s what you’ve got!"

"By St. David, if I catch you, I’ll----" cried the now exasperated Welshman.

"Abnormal circumference--distended stummick, that’s what you’re sufferin’ from. The capten says so!" replied Gadget as a parting shot.

This ungentle reference to his personal symmetry was too much for the engineer, and he made another wild rush in the direction of his opponent. This time, Gadget had no opportunity to lock the door, but, turning round, he bolted precipitately down the long keel corridor, cannoning into the chief officer, who was just coming along to the rear gondola, and receiving a somewhat violent cuff on the head from that dignified official, whose gravity had been gravely endangered by this sudden encounter.

"Here, you little rascal, take that!" cried the angry officer, and Gadget, glad to get away on such slight terms, and feeling that he had given his opponent value for his money, scampered off, and made his way to the wireless cabin.

Here he assumed immediately an attitude of respectful attention, and even prevailed on the officer in charge to give him another lesson on the Morse code, for the urchin had a wonderful range of feeling which enabled him at a moment’s notice to adapt himself to the circumstances of his environment.

"Wonderful, Gadget! You’re making rapid progress. You shall have a lesson in taking down messages, to-morrow. You have the making of a good wireless operator in you. I shall speak to the captain about it."

"Thank you, sir," replied the _gamin_, pulling his lock of hair by way of salute. This lock of hair, by the way, at the urchin’s special request, had been left there, when the famous "R. D. clippers" had shorn off the rest of the crop, when the airship’s barber had overhauled and close-reefed him, soon after his first encounter with the captain.

Gadget’s next visit was to the little photographic cabin, where the wonderful negatives and bioscope films were carefully prepared. These were to record to the world at large the wonderful panorama of the earth and sky, photographed from the great air-liner on her wonderful trip.

Here, again, by his artful, winning way, which Gadget knew how to adopt when circumstances demanded it, the little urchin was on good terms with the photographic officer. The latter, who admired the boy’s character and wit, and pitied his upbringing, had declared more than once that Gadget possessed in a large degree that intuitive genius which belongs to greatness, and prophesied a brilliant future for the neglected boy, if only he could be properly trained.

"Come to me for an hour a day, Gadget, when the captain does not require your services, and I will teach you photography. Some day you shall have a camera of your own, and who knows, you may become a great film operator." And the grateful boy was only too quick to learn what these skilful operators had to teach.

So, into this new life of adventure and travel, this little urchin entered with all the zest and enthusiasm of which he was capable, making many friends, and an occasional enemy. And all the while the great airship, glistening in the tropical sun, sailed on across the wide stretch of desert which lies between India and Egypt, along the line of the thirtieth parallel.

*CHAPTER VIII*

*SONS OF THE DESERT*

The tropical sun looked fiercely down upon the burning sands of the Hamadian Desert. North, south, east and west, as far as the eye could reach, in every direction, the illimitable waste of desert stretched, save only at one pleasant, fertile spot, where a cluster of date and lofty palm trees fringed the banks of a silent pool.

A small encampment of Bedouins, sons of the desert, fierce-looking and proud, occupied this charming spot. Three small tents and a larger one, a camouflaged fabric, part of the loot of the garrison of Kut, completed the camp. There were a dozen men all told, and as many noble, fiery Arab steeds. The men were well armed, with modern weapons, too. There had been too much loot in the Mesopotamian campaign during recent years for the Arab sheik and his followers to find much difficulty in securing the very pick of European weapons, ammunition and equipment. But one thing was evident--all these men were not real sons of the desert. Three of them at least were Europeans, as the reader will shortly perceive.

An atmosphere of subdued excitement, primed with expectancy, seemed to pervade the camp. The whole party were eagerly watching and waiting for something. But what caravan, with its tinkling bells, its camels and spices, its rich silks and ladings from Persia or from Damascus had awakened the predatory instincts of these kings of the desert? Besides, were they not too few in number to engage a well-armed band of Baghdad merchants?

Nay, it was no rich argosy of the desert that these fierce men expected; their eyes were directed one and all towards the skies, for the days had now arrived of which the poet spoke, when he

"Saw the heavens filled with commerce, Argosies of magic sails, Pilots of the purple twilight, Dropping down with costly bales;"

and they were awaiting, with evil intent, the passing of the Aerial Mail, which they knew to be carrying vast treasures of gold and other precious things from India to Cairo and Europe.

The three Europeans who had collected and organised these robber chiefs, by appealing to their hereditary instincts, were none other than our friends, Rittmeister von Spitzer, and his companions Carl and Max, the German irreconcilables, whom we left in the dark shadows of the Schwarzwald preparing for their adventure.

Already they had made a name greater than Muller of the _Emden_, but they had made themselves outlaws of the nations of the world, and though for a little while success and fame might attend them, yet they knew that sooner or later the agreed price of their adventure would be death.

"What news of the British air-liner, Max?" called von Spitzer, as his subordinate descended by a rope ladder from one of the smaller trees, where an observation post had been fixed, and an aerial mounted, for the purposes of wireless telegraphy and telephony.

"She left Delhi at mid-day yesterday, sir," replied the operator, unclamping the receivers which till now had been fixed over his ears.

"Then she’s running to scheduled time?"

"Yes, sir."

"Was it the official departure message that you tapped?"

"It must have been, Rittmeister, for it announced that a distinguished passenger had joined her at the last moment."

"Indeed! What was his name? Did you discover it?" asked the flight-commander, who, to maintain his influence over the wild sons of the desert, was wearing the loose, flowing robes of an Arab sheik, richly emblazoned and adorned.

"His name was the Maharajah of Bangalore," replied Max, the erstwhile Gotha pilot.

"What! the miscreant! He was the man who raised thirty thousand Indian troops for the Mesopotamian campaign, and made it possible for the British to advance on Baghdad after their disaster at Kut."

"That accounts for it. He is to be decorated at St. James’s Palace for some eminent services he has rendered to the British Government."

"We’re in luck’s way, Max. I may spare his life, as I do not seek to take any man’s life who does not oppose me. But it’s a thousand to one he’s carrying his jewels and his household gods with him; it is the custom of these eastern potentates. I will strip him as the locust strips the vine. I will give his jewels to these brave Arabs; it will confirm my hold upon them. We may need their help upon another occasion. But, this is by the way, was there anything from the professor?"

"Only this, Rittmeister; I have waited since dawn for it," and the operator handed to Spitzer a cryptic message of seven letters, which, to the receiver at least was quite unintelligible. Max had pencilled it down as follows:--"X--G--P--C--V--S--M," for it had come through the ether by wireless telegraphy and not by wireless telephone, like the first message. The reason was obvious. One message was for public intelligence and for use in the newspapers, and the other was for more secret and sinister purposes. The cryptogram had come from the professor, who, with his mechanic, had been left behind in the Schwarzwald to collect information for the brigands, and to obtain further supplies of uranis for the _Scorpion_.

The Rittmeister eagerly grasped the little strip of paper on which the message was written, and retired to the small hangar where the _Scorpion_ was pegged down and stowed away, remarking:--

"This is evidently urgent; I must get the cipher-key and decode it at once. Meantime, I want you to rehearse the men in the parts they are to play, and give Carl a hand with the vibration drum. The great liner is almost due. You may tell the sheik that in addition to the large cargo of gold which the airship carries, an Indian Prince with jewels worth a king’s ransom is on board."

"Your orders shall be carried out, Rittmeister," replied Max, who was glad to be relieved of his monotonous task of listening hour after hour for coded messages, and looked forward with some pleasure to the coming adventure.

Shortly afterwards, Max, having delivered his message to the Arabian chief, was standing beside Carl under the shadow of a cluster of trees on the very margin of the pool. That wonderful instrument, the vibrative drum, which is fashioned somewhat on the principle of the human ear, but with a large horn-shaped receptacle for receiving the very minutest sound waves, and focussing them on to a very sensitive drum, was engaging their attention.

Every now and then, when they fancied they heard a sound that broke the stillness of the desert, they would listen acutely, turning the horn this way and that way to discover whence came the sound.

"They are due about mid-day, the chief says," remarked Carl, after a brief pause in their conversation. "What time do you make it now?"

"A quarter of an hour yet," responded Max, consulting his chronometer, and making a rapid calculation to allow for the difference in longitude, for he still carried Central European time.

"And they’re sure to follow the 30th parallel?"

"Yes, it’s their shortest route," replied the wireless expert.

"Then they should pass within three or four miles from here," observed Carl.

"Yes, unless they’ve drifted a little out of their course."

"But we should hear them on the vibrator even if they were fifty miles away in a silent land like this."

"Undoubtedly."

"Listen! Can you hear anything?" exclaimed Max in a slightly nervous tone, after a brief silence.

"No, I don’t think so, but those fellows over there must be quiet; they’re getting excited about the promised loot."

"Go and tell them, Carl; you speak the best Arabic."

The German left the drum for a moment and after expostulating for a while with the sheik, he gained his point and the word was passed along for silence.

The Arabs were greatly mystified by this strange instrument, as well as by those aerial wires affixed to the trees, and most of all by that strange, weird machine, hidden away behind the sand-proof curtains of the little camouflaged hangar, like the sacred ark in the holy of holies.

With wondering eyes they had on occasion watched the _Scorpion_ mount to the heavens with marvellous ease and descend with like facility--bearing its human burden aloft to the very skies and bringing them safely to earth again.

These strange gods which the infidels had brought with them to their desert home were greatly feared even by these brave, proud men, and it was only the largesse and the promise of still better things to come, from the great white chief, which prevented these sons of the desert from leaving this dreaded spot.

The scout pilot, having obtained his wish, now returned to the instrument, for his companion was already beckoning to him. Evidently the approach of the airship had been indicated by the sensitive drum, but, ere Carl reached the margin of the pool, he noticed the Rittmeister emerge from the hangar where he had been decoding the message, and wave for him to approach.

"What is it, Rittmeister?" he called.

"The message. Come here a moment!"

Max, who thought that a faint sound he had just heard from the instrument might portend the distant approach of the liner, left the drum, for he knew there would be plenty of time, and joined the other two by the hangar on the other side of the pool, for he also was curious about the cryptic message, which he had taken earlier in the day.

"Was it from the professor?" he asked in his first breath.

"Yes, he is in for a bad time, I fear," replied the Rittmeister. "He will not be able to communicate again for some time."

"What is the matter?" asked the others simultaneously.

"Why, Keane and Sharpe are on his track again. You know the rascals; they were secret service pilots and spies during the war, and now they are scout pilots in the British aerial police. They’re the left-hand and the right hand of that confounded Tempest, the little tin god at Scotland Yard, and the brains of the aerial police."

"Himmel! I hope he can outwit them," exclaimed Carl. "They’re keen birds, both of them, and they have some exploits to their credit."

"If he can’t, then the length of our existence is the capacity of those remaining eight cylinders of uranis," ventured Max.

"And the length of the rope round our necks as well," murmured his companion.

They all laughed at this, but Spitzer looked keenly for an instant into the eyes of the two pilots, as though he would search their innermost souls, and make sure that they would be game to the end. But they evidently read his thoughts also, for Max announced:--

"It’s all right, Rittmeister; we’re not going back upon our word. The die is cast!" and Carl in a brave attempt at another sally, added:--

"The cast is--die!" at which they all laughed again, as the old sea pirates laughed before they blew up their ship, when they saw that the game was up.

The next instant their thoughts were diverted to another subject. It was already mid-day, for the sun by his altitude announced it. As they approached the drum, they could now distinctly hear the hum of mighty engines though still forty miles away, recorded in that delicate instrument, and one thought, uttered or unexpressed, came instinctively to each mind:--

"Aircraft approaching!"

*CHAPTER IX*

*THE PHANTOM BIRD*

"Airship or aeroplane?" asked von Spitzer, a moment later, as Carl closely watched the delicate recorder, which, as the vibration caused by the sound waves increased, indicated not only the type of craft, but the type of engine by which it was driven, and also whether the engine was running with or without defects. So wonderful are the secrets which man has already wrested from nature.

"Airship, decidedly!" replied Carl, after a second’s pause. "Full-powered too; there are four or five Sunbeam-Maori engines, and all running smoothly."

"Her position?" demanded the Rittmeister next.

"Forty-four miles due east," came the answer.

"Then it must be the aerial mail from India; she is just about due."

"Is she steering due west?" the chief asked.

"About two degrees south, that’s all," replied Carl. "She’s evidently getting a little drift from the upper currents."

"Good!" remarked the chief airman. "Then if she continues steering steady, she should pass within a couple of miles of us in another twenty or twenty-five minutes. Come along, Carl, it is time for us to get away. You will remain on the ground, Max. You have a difficult job. As soon as we get away, see that the tents are struck, and all men and horses placed under cover of the trees."

"Yes, sir."

"And now sound the alarm signal, and help us to get out the _Scorpion_; it is going to bite to-day," ordered the Rittmeister as he strode away, exclaiming,

"Who wouldn’t be a king of the desert? For one day at least it will be, ’_Deutschland, Deutschland ueber alles_!’"

The alarm being sounded, all the occupants of the little camp went to quarters, just as they had been rehearsed during the last few days. The camouflaged fabric was stripped from the little hangar, and the _Scorpion_ was set free to bite once more. She was released from the ropes which held her down and turned head to wind. The steel folding wings were snapped back into their sockets and made secure.

"Are you ready, Carl?" asked the chief, as he completed his rapid survey of the machine, during which neither the propellers, planes, tail-fin nor rudder escaped his scrutiny.

"Aye, ready, sir!" came the reply from the junior, who was now seated in the armour-plated conning-tower, testing the controls and examining his machine guns.

Without a moment’s delay the chief clambered up through the little trapdoor and joined his companion. Then he paused for a moment whilst he swept the eastern horizon with his powerful binoculars.

"I cannot see her yet, Carl," he said. Then turning to Max, who stood by the starboard engine, he shouted, "Just try to pick up her position again from the drum. She may have changed her course a trifle."

The Gotha pilot dashed off on his errand, and after carefully listening for a moment, he returned and said, "East-south-east, about four degrees east."

"Good, she’ll pass about five miles south of us then; but she’s not visible yet," replied Spitzer.

"She’s getting a good deal of drift, I fancy," returned Max.

"Anyhow, we’ll get up into the blue and wait for her," said the airman, and waving his hand for the signal to stand clear, he pressed the self-starting knob, and instantaneously both engines sprang into life, and the whirring propellers started up such a dust storm from the loose sand of the desert that the Arabs were startled, and rushed to secure their frightened steeds.

Within ten seconds the rev.-counter indicated two thousand five hundred, and, sufficient power for flying speed being thus obtained, Max deftly removed the chocks from the wheels, and this new type of desert steed dashed off across the sands, and leapt into the air, amid the cheers of the astonished Bedouins.

"Allah, the Compassionate, the Merciful!" cried the Arab chief, as he raised his hands imploringly towards heaven. "It is the bird of destiny, my children, the phantom of the desert!" and Max could scarcely restrain a smile as he beheld the momentary fear which had seized these strong, fierce men.

The next moment, however, they were all busy striking the tents and bringing horses, equipment, and all the camp effects under the shadow of the trees.

Meanwhile the _Scorpion_, appearing exactly like a huge grey phantom bird, soared away in a north-westerly direction, lest it should be observed by the occupants of the approaching liner.

And in a few minutes, rising rapidly by steep spirals, and an almost vertical climb, it had disappeared from sight. Soon it soared over the camp again at ten thousand feet, and appeared but a speck in the cloudless blue, like the faintest suspicion of a tiny cirrus cloud.

Shortly afterwards a cry from one of the natives directed the attention of all present towards another tiny streak in the opposite direction. His sharp, piercing eyes had been the first to discern the approaching airship.

"Allah, the Compassionate!" again began the sheik, and Max, fearing that this strange visitant might affect their nerves, called out aloud in the best Arabic he could muster:--

"Allah be praised! This stranger carries gold and rare jewels across the desert. He must pay tribute to the sons of Jebel and Shomer!"

This appeal to their cupidity instantly changed the demeanour of these fanatics. Their fear departed. Even when, later, they heard the roar of the powerful engines which propelled the airship, their one thought was of plunder.

"The treasures of twenty Damascus’ caravans are in that great airship," cried Max, fulfilling with considerable skill the part which Spitzer had allotted to him.

The Bedouins, whose feelings were now raised to the highest pitch of excitement, began to fear lest, after all, so rich a prize might be lost, and they eagerly searched the skies for the phantom airman, as they called the Rittmeister, and shouted:--

"Where is the phantom bird? Where is the great white sheik?" and they would have dashed out into the desert on their fiery steeds, for they were already mounted, but the German restrained them, saying:--

"There is no need to hunt the quarry. The great white sheik will bring down the airship on this very spot. Be ready, when I give the signal, to surround it."

Another anxious moment passed, and the airship, travelling rapidly at some three thousand feet above the ground, would have passed them by some few miles to the south, but at that instant, the Indian judge caught sight of the picturesque oasis with its cluster of palms far down below, and said to his soldier companion:--

"Look, Colonel Wilson! Just look at that beauty spot after two hundred miles of yellow desert."

"Ah, wonderful!" exclaimed the delighted soldier. "It is a little garden planted by Nature in the solitary wastes."

"How picturesque! I should like to land there," returned the other.

"Let us ask the captain at least to change his course slightly, so that we may pass over it and photograph it as a souvenir of our pleasant journey," said the officer.

At that moment the captain, passing down the gangway, overheard the remark, and being eager to oblige his distinguished passengers, he telephoned his orders to the navigating officer, who slightly altered the ship’s course, so as to pass almost directly over the oasis.

It was while they were engaged in delightful contemplation of this emerald isle embedded in the gold of the desert, that another object attracted the attention of the judge. Chancing to glance upwards, he caught sight of a silvery speck six thousand feet above them, and a little way on their beam.

"See, a tiny cloudlet in the sky; the first I have ever seen in crossing these deserts."

"A cloud, where?" asked his companion.

"There, right up in the blue vault of heaven," said the judge, pointing out the speck which now seemed to have grown larger.

"Why, it is a bird; some great vulture of the desert. It seems to be diving right down upon us! These vultures, I hear, have often attacked the airships in the desert. It evidently takes us for some new kind of prey."

"A bird!" cried the captain, who had now joined the speakers. "Let me see it?"

"There it is!" cried the two men simultaneously, pointing out the grey, swift phantom.

The captain saw the bird-like object, and one glance sufficed.

"It is an aeroplane," he said, and there was just a touch of uneasiness in his voice.

"An aeroplane?" echoed the others, and an instant later, viewing it through his glasses, the colonel added:--

"Why, so it is; but I say, Captain, what a peculiar type of aeroplane! It is one of the patrols, I expect, come to meet us."

"Your glasses, if you please, for one moment," asked the captain, and he almost snatched them from the hands of the officer.

The next instant a violent expletive burst from the captain’s lips.

Leaving his companions, he dashed down the corridor to the wireless operator’s room. The operator was already engaged in conversation with the aerial visitor by means of the wireless telephone, and the captain took in the situation at a glance.

"What does he want? Who is he?" blurted out the skipper.

*CHAPTER X*

*THE BRIGAND OF THE EASTERN SKIES*

"Someone has signalled us to stop, Captain!" said the wireless operator.

"Who is it?" demanded the irate skipper.

"He will not declare himself, sir!"

"Hand me that receiver, Robson!" and the commander, clamping the ear-piece of the wireless telephone to his ear, asked of the intruder, "Who are you that thus dares to order me to stop on a lawful voyage?"

"It is I, Sultan von Selim, Air-King of the Hamadian Desert, who orders you to stop!" came the reply from the aerial raider, who now rode just a little way above the large airship, and on the starboard side.

"Then I refuse!" thundered the skipper.

"You will do so at your peril," came the quiet, cool reply, which rather disconcerted the captain.

"I will call up the patrols, you brigand!" continued the commander of the liner.

"One word to the patrols and I will blow your wireless to pieces. I have two guns already trained on it," replied the air-king.

"I dare you to do it!" replied the brave skipper. Then, turning to the operator, he said, "Send the S.O.S. with the latitude and longitude to the patrols. Smartly there, Robson."

"Yes, sir."

"This is that raider we heard of at Delhi, but he can’t touch us."

The raider, however, had caught the sentence, or part of it, and he understood the order. The next instant a burst of fire from a machine gun, trained with wonderful accuracy, blew the main part of the wireless apparatus to pieces, and rendered it perfectly useless for either receiving or transmitting. How the captain and the operator escaped injury or death will for ever remain a mystery.

Seizing a megaphone, the former dashed out of the cabin, down the keel corridor and the narrow slip-way, to the central touring gondola on the starboard side, and, shaking his fist at the raider, who sailed calmly alongside about a hundred feet away, shouted through the instrument: "You brigand! You shall hang for this!"

A mocking laugh, drowned by the roar of the engines, which still continued full speed ahead, was the only reply. Evidently this mad airman was enjoying the fun immensely. At any rate he appeared very careless of the other’s threats.

"I mean it, you felon!" roared the skipper.

"Are you going to heave to?" came the the reply through the raider’s megaphone.

"No, certainly not!"

"Then you must take the consequence!" came the mocking taunt, and the next instant, "Rep-r-r-r-r-r-r-r!" came another burst from that deadly machine-gun, which seemed so effective every time it spoke.

This time the starboard engine, a 250-H.P. motor, conked out entirely, and, for a moment, there was danger of fire in the gondola, owing to the petrol-feed being smashed in the general break-up.

This made the captain think furiously. He now recognised, for the first time, that he was absolutely at the mercy of this strange highwayman of the air. Evidently he was a determined character, a master criminal, and the skipper looked round for some means of defence.

There was certainly an old machine-gun aboard the airship, but it had never been used and was not even mounted, for it was believed that a peaceful trader would never need it. The police patrols constituted the real defence of the trade routes, and even with them a few smugglers were the chief offenders.

The captain’s eyes were fixed for the next few seconds on the wonderful machine which sailed along so easily and so quietly. Once, he had noticed, when the raider made a circuit of the great liner, that the machine had shot ahead at twice or thrice the speed of the _Empress_. The armoured conning-tower, over the top of which the heads of the pilot and his companion could just be seen, gave the skipper an impression of strength, against which he knew that even if he could have replied with a machine gun, the bullets would have pattered harmlessly against the sides, and fallen away like rain-drops.

He was in a quandary, this brave air-skipper. He had missed his chance of calling up the patrols. Yet, how could he, a British captain, surrender to some foreign marauder, or perhaps even to a British renegade; for he knew not as yet who this bold fellow was. Then he thought of his passengers, those distinguished guests committed to his charge, and last of all of the valuable lading: that consignment of gold for the vaults of the Bank of England.

"By heaven, it’s the gold they’re after!" he exclaimed. "I never thought of it before. They’ve had the news ahead of us and they’ve waited for the airship in this out-of-the-world spot. Confound them, but they shan’t get it if I can help it!" and the captain nerved himself to still further resistance, though he felt it was hopeless, unless some outlying patrol should come up quickly.

The raider seemed to have read his thoughts, for he sailed close up again, and shouted through his megaphone, "For the last time, Captain, will you heave to?"

"No--o!" the courageous man replied, though this time his voice wavered a bit, for he wondered what devilry the stranger would attempt next.

He had not long to wait, for the pirate suddenly banked his machine, turned swiftly outwards, and circling round till he came up level with the great twin-engine in the rear gondola, which drove the giant propeller near the rudder, he opened once more a terrific burst of fire which instantly put both engines out of action.

This almost brought the huge liner to a stop. At any rate, she now made more leeway than headway, for the only remaining engines which could now be used were those in the foremost gondola and port centre cabin.

"Stop!" signalled the captain to the remaining engineers in charge of those engines.

And the next instant the huge, looming mass, with her engines silent, lay there helpless, levering away to windward, shorn of her pride, and with the wreckage hanging loose from her rear and central gondolas.

Another surprise that now awaited the crew and passengers of the air-liner was to see the phantom raider careering wildly around the beaten giant at enormous speed, in almost perfect silence, though his two propellers raced wildly as he dipped, spun and rolled to celebrate his victory, and to show off his amazing powers to the victims.

"Good heavens!" ejaculated the captain as he watched all this. "It was only too true, then, what we heard at Delhi."

"You mean about the silent engines and the speed of three hundred miles an hour," added the navigating officer, who now stood by the skipper.

"Yes. It’s some amazing conspiracy. I cannot help admiring the rascals, though I should like to hang the pair of them."

"Hullo! here he comes again. I wonder what he wants this time," and the next instant the raider throttled down, and came close up to the gondola, shouting as he did so in perfectly good English:--

"Start that port engine, please, and bring her to earth by that cluster of palm-trees over there."

"What more do you want with us?" replied the captain.

"I must see your passports, and examine your cargo for contraband."

"Eh, what’s that?" exclaimed the amazed commander. "What does he want to examine our passports for?"

"We haven’t any," remarked the navigating officer.

"And why the deuce is he to search for contraband, I should like to know?" groaned the skipper.

"Did you hear what I said?" called the raider, who now appeared to be getting angry at the delay.

"Yes," growled the other.

"Then bring her down at once, and let out that mooring cable!"

And as there was no apparent help for it, and not a single patrol had yet hove in sight, the captain of the liner reluctantly complied, wasting as much time as he dared in the operation.

*CHAPTER XI*

*THE AIR-KING’S TRIBUTE*

Far down below, the Arab sheik and his party, ambushed amid the waving palms of the oasis, had watched with keen and eager eyes this thrilling encounter in the heavens between the phantom-bird and the great leviathan. To them it seemed impossible that the aeroplane, sometimes diminished by distance to a tiny speck, could overcome the mighty airship.

As the fight continued, and they heard the rat-tat-tat of the machine-gun, sometimes their doubts and fears overcame them, and many were the cries that went up to Allah the Compassionate, the Faithful, etc. But when they saw that at last the great white sheik had won and the disabled liner was slowly coming lower and lower, their pent-up feelings gave place to wild excitement, and shouts of,

"Allah be praised! The bird of destiny has won! The great white chief has triumphed!" while others, more practical, and also more piratical, exclaimed: "Allah is sending down the treasures of heavens into the lap of the faithful. Praise be to Allah and to Mohammed his Prophet!"

It was with some difficulty that Max restrained these wild men from dashing out in their frenzy to capture and loot the huge, lowering mass that now loomed but a little way above them. He began to fear that they would not wait for the pre-arranged signal, and he urged the Arab sheik to restrain them, and to repeat the orders that the occupants of the airship must not be touched.

Nearer and nearer came the huge mass, steering badly and veering round in attempting to gain the lee-side of the trees, lest she should be totally wrecked in the mooring. Two hundred feet of cable suddenly dropped from her bow, and, when it touched the ground, Max gave the signal, and with a wild shout these fierce Bedouin horsemen suddenly broke from cover, and galloped into the open.

"Ye saints!" gasped the Indian judge, when he beheld this wild tournament of galloping horsemen, brandishing their rifles and long spears. "Are we to be eaten alive?" Less than an hour ago he had expressed a pious wish to visit this peaceful garden in the desert; now, it was too near to be pleasant.

"All hands to the cable!" shouted Max in Arabic, and very quickly both horses and men were struggling with the stout hawser.

"This way," shouted the Gotha pilot. "Take it round and round these three trees; they should stand the strain unless the wind gets stronger," and selecting a small group of trees on the leeward side of the grove, he very quickly had the cable made fast in such a way that the leviathan of seven hundred feet in length swung easily head to wind, like a ship riding at anchor and swinging with the tide.

Then the tribesmen, kept well in hand, surrounded the prize, keeping some thirty paces distant, for they had not yet quite overcome their fears. Never before had such a thing been seen resting on the yellow sands of the Hamadian Desert.

As the gondolas of the _Empress of India_ came to rest quietly on the ground, the _Scorpion_ descended in a rapid spiral, touched the sands lightly and taxied up to the fringe of trees.

Then, to the utter amazement of the occupants of the dirigible, some of whom were already descending from the gondolas, a couple of men, wearing the loose flowing robe of the desert, including that distinctive mark of the Mohammedan world, the fez, leapt from the machine and approached the airship.

"Snakes alive!" ejaculated the colonel; "but what have we here?" his eyes fixed upon the two men.

"Some person of note, evidently," remarked his friend the judge, as he saw the foremost of these individuals mount a richly caparisoned horse which was held in readiness for him, and approach in a dignified and almost royal manner.

"This king of the desert is evidently some European renegade who is challenging the right of other nations to cross his domain without his permission," said the soldier.

"He is some daring pilot, at any rate," replied the justiciary.

"I wonder now what he intends to do with us," observed the other.

"Why, he intends to plunder us, of course," replied his companion. "What else could be his motive?"

The captives were not long to be left in doubt as to the proceedings of this daring freebooter. Raising the megaphone which he had used in the air so effectively, he shouted in perfectly good English:--

"Abandon airship!"

And to make this order immediately effective, the desert king ordered Max to see that every member of the great liner, passengers and crew, were immediately assembled before him. The navigating officer and the captain were the last to leave the vessel; they did so unwillingly, and not without a measure of compulsion at the point of a revolver. The skipper’s looks as he fixed them upon this desert freebooter astride the fiery steed, conveyed to the brigand much more than mere words could have expressed.

Fixing him with his keen, malicious eyes, the pirate said: "Are you the captain of this vessel?"

"I am," replied the skipper in surly tones.

"Show me your bill of lading."

"Bill of lading?" echoed the captive. "You must hunt for it if you want it."

The self-styled king of the desert frowned. He knew that he was up against an English skipper, and that he must adopt other measures to gain his end. Without lifting his gaze from the commander of the air-liner, or flinching a muscle, he replied firmly, "One word from me, Captain, and your life would be forfeit. You would swing from that tree by one of your own cables."

"I know that, brigand," replied the prisoner. "Get a cable and carry out your threat; the rope that will hang you is not so very far away, either."

"Very well," exclaimed the German. "Then, I need only give the order to these, my faithful subjects, and the whole of your valuable cargo will be strewn on the sands, and your airship will be alight. I do not propose to adopt those measures unless you compel me. I will give you five minutes to decide." As the pirate uttered these words in a cool, nonchalant manner, he glanced at the European emblem on his wrist, a gold, gem-studded wristlet watch with luminous dial.

"I deny your right to interfere with a peaceful trader," blurted out the captain, when he saw the full force of the two alternatives which had been offered to him. He was wondering, moreover, how much the brigand knew about the presence of the specie on the vessel.

"You deny my right, do you?" returned the other.

"Yes. Who are you?"

"I am Sultan von Selim, Air-King of the Hamadian Desert. I told you that once before when I first challenged you in the air."

"Who made you king?" snorted the captain.

There was silence for the space of ten seconds, during which time the brigand consulted his watch again, then replied:--

"The Allies made me king, particularly you _verdammt_ English when you drove me from my Fatherland with those impossible peace terms. King I am, and king I will remain, of all the aerial regions where I choose to abide, until there comes a better man who can beat me in the air. And you, Captain, of all men, must know from what you have already seen that my powers in that realm are considerable."

The captain, having cooled somewhat after this outburst, had to admit to this German irreconcilable that there was certainly some truth in his statement about being king of the air. Certain things were beginning to dawn upon this English captain, and he was now wondering how far it would be wise to humour the brigand. He added, however, to his admission, the following words, "You are only king by might!"

"Ha! ha!" laughed the outlaw, "but that also is some admission. My position is precisely that of the British in India or Egypt. Withdraw your soldiers from these two countries and what becomes of your government there? So am I King of the Hamadian Desert till a stronger man comes. When that time comes one of us must die. There is no room for two kings, even in the desert. Till then I am supreme. But come, captain, four minutes have passed already. Your bill of lading, quickly now, for we are but wasting time, and these my subjects"--and here the brigand waved his hand towards the restive Arabs--"or rather I should say my customs’ officials, are waiting to examine your cargo, and to levy the king’s tribute."

The captain looked around first upon his own followers and then upon the impatient Bedouins--the vultures around the carcase.

"I could have brought your ship down in flames, but I preferred a milder method," continued the outlaw, as he watched the seconds of the last minute being ticked away on his jewelled watch.

"But helium will not burn!" returned the captain smartly. "That was beyond your powers."

A mocking, sardonic laugh came from the robber chief as the Englishman uttered these words.

"Would you like to see it burn?" he almost hissed.

The captain faltered in his reply; he was not quite so decisive as he had been. Evidently there was some sense of humour, if not much, about this irreconcilable German.

"Here, Carl!" cried the bandit. "Detach one of those nineteen ballonettes from the airship."

"Yes, sir," replied the subordinate, stepping up to the king and saluting smartly.

"Take it away to leeward there, and show this dull Englishman how he may learn chemistry and science even from inhabitants of the Hamadian Desert. Here, take this, you will need it," and the chief handed to his assistant a small cylindrical tube with which to carry out his orders.

Turning next to the Englishman, he observed, "Know, you dullard, that a small admixture of a secret gas, which is known only to three living men, will make your renowned helium flare like hydrogen. You shall see it in a short space of time."

"Recall your man, I will take your word for it, Sultan!" exclaimed the captain, who now felt that it must be so, for he was already bewildered by the strange things which he had witnessed that day, and he had no desire to see this experiment carried out.

"You believe me, then," returned the air-king, who seemed particularly to relish this interview with the Englishman, especially with this group of celebrities within earshot, for they had listened eagerly to every word which he had spoken. And the German knew that though his days might be numbered, as indeed he felt they were, yet his fame would be greatly enhanced by the episodes of this day, for vanity was not the least among his failings.

Once more he glanced at his watch; for the allotted space of time had nearly run.

"How now, Englishman!" he exclaimed in a harsher tone. "The bill of lading, where is it?"

The chief purser, receiving the captain’s nod, at once advanced towards the regal horseman, handed him a bundle of papers and said: "Here, sir, is the document you desire."

*CHAPTER XII*

*THE MAHARAJAH’S CHOICE*

A dramatic episode followed the examination of the airship’s bill of lading by the _pseudo_ monarch and his so-called chancellor of the exchequer, Carl, who aided his master in the task.

"Item one. What does that consist of?" asked the brigand.

"Mails. His Britannic Majesty’s mails," replied the chancellor.

"Where from?"

"From India for Egypt and London," replied Carl, maintaining a grave and solemn deportment.

"H’m! They may pass when the usual tribute is paid," remarked the bandit in serious tones, as though he had delivered himself of some weighty pronouncement.

The judge looked at the colonel with raised eyebrows when he heard this strange decision, but the captain, forgetting his position for a moment, blurted out:--

"Tribute indeed? When did the King of England pay tribute for his mails to be carried across the Hamadian desert?"

The air-king eyed the speaker with apparent amazement, mingled with a touch of scorn and pity, then quietly observed:--

"That is the very point, Captain. There has been far too much laxity in this respect in the past. The liberties of the small nations to make their own laws, and possess their own lands in peace, have been greatly endangered of late. It is mere brigandage for a great power to over-ride the native interests of small communities. But from to-day this brigandage must cease, at any rate over the territories where I rule."

The captain could find no reply to this sally of the desert king’s, and, while a smile played about the corners of his mouth, he looked beyond this robber chief, in his gaudy trappings, to where the _Scorpion_ lay squatting like an ugly toad upon the sands.

At length the monarch resumed his cross-examination with these words: "Come, Captain, will you pay tribute for the transit of mails across my territory, or will you not?"

"I will not!" replied the skipper.

With a flash of fire in his tones the brigand ordered: "Take the first ten sacks of mails out into the desert and burn them at once."

"It shall be done, O chief," replied Max, who immediately detailed some of the natives to carry the order into effect, when the captain, urged to it by the judge, asked:--

"What is the amount of the tribute?"

"Ten thousand pounds in English gold," came the immediate reply.

"I cannot pay it," returned the captain. "It is mere plunder," though the judge pointed out to the commander quietly that it would probably be more profitable to pay it and to get away with the mails in a damaged airship, than to leave the mails behind to be lost or destroyed in the desert.

"He will take the gold anyhow, when he comes to it on the bill of lading," added the colonel, "though devil a penny I’d pay him."

"It isn’t my money," argued the captain, "so there’s an end of it."

"How now, Englishmen! We are wasting time. Will you pay the sum demanded?"

"No, I will not!"

"Very good. Get out the rest of the mails and burn them at once!" ordered the monarch, and a couple of minutes afterwards the first bags of mails, sprayed with some inflammatory liquid, were blazing furiously.

"Item two!" called the desert king.

"Gold. Nineteen boxes of bullion for the Bank of England," called out the chancellor.

"Gold?" echoed the air-fiend, as though he were utterly unconscious of the presence of such a commodity, in face of the captain’s refusal to pay over a trifling ten thousand pounds to secure right of way for his mails.

"Yes, sir. Nearly one hundred thousand pounds in specie."

"I thought we had prohibited the importation of gold into these regions, chancellor, because of its evil effects upon the minds of the people."

"Yes, sir," returned the chancellor. "We decided to abolish its importation altogether on that account, save only as tribute money for the royal chest."

"Exactly," replied the bandit, in a tone of assumed moral injury. Then, turning to the Englishman, he said: "You must know, Captain, that most wars are caused by gold, and by the unbrotherly strife which it foments. You must know also that all wars are sustained by it."

"Yes, I agree with you for once," returned the prisoner, boldly, wondering at the ease with which this confirmed brigand could turn moralist.

"Then what must be done with the gold, sir?" asked the chancellor.

"Every ounce of gold on the airship must be confiscated," exclaimed the king of robbers as he uplifted his hands in pious horror. "Let it be removed at once."

"Very well, sir," and this second operation, which was more pleasing still to the waiting Arabs, was immediately put into effect.

"Item three!" called out the chief.

"Ten boxes of valuables, including the personal property and belongings of one of the passengers," came the reply.

"What, do they belong to one person?"

"Yes, sir."

"What is his name?"

"The Maharajah of Bangapore, sir," returned the wise man of the exchequer, whose task promised to be an easy one in the future, judging by the vast amount of spoil which had already fallen into his lap.

"The Maharajah of Bangapore?" repeated the monarch, raising his hand to his forehead for an instant, as though he would recall some long forgotten episode. "Is he amongst the company present?"

"I believe so."

"Ask him to stand forth."

And the Indian prince, hearing his name called in English, stepped forth and confronted his old enemy of the Mesopotamian campaign. When their eyes met a flash of fire, more eloquent than words, revealed what was in each man’s mind. The prince expected to be tortured to death and was prepared for it, for, like all his people, he was brave as well as fierce. At last the robber spoke.

"Prince Jaipur, you are an enemy of mine," he said.

"I know it!"

"Do you expect mercy after the way your tribesmen massacred my men at Kerbela?"

The maharajah shrugged his shoulders, but disdained to reply to this upstart robber chief who styled himself a king.

"Do you know that your life is in my hands?" exclaimed the bandit fiercely.

"I am not afraid of anything you can do, brigand!" hissed the prince, and his voice sounded not unlike the angry, venomous snake in the jungle. Another man might have quailed before those glaring eyes and those hissing tones. But the German quavered not.

"I will give you a kingly choice," he said, "as you are the scion of half a hundred kings in your illustrious line."

"I ask no favours of a common Bedouin robber," snarled the other.

"Listen. I will give you the choice of drinking this deadly poison, or of being dropped ten thousand feet from my aeroplane. Which will you take?"

The prince shuddered slightly, and glanced up into the cloudless blue, as though anticipating what such a death might mean, then looked at the small phial which the brigand held forth in his hand.

"Yes, ten thousand feet!" continued the German, as he noted the anxious look which overcast the Hindoo’s face for an instant, as he gazed up into the sky. "Then I will loop the machine, and, with your hands pinioned, you will be thrown out and drop, drop---- Which will you choose?"

"I will drink the poison," replied the prince, who had now regained his usual composure.

"Very well. Let him be securely tied to that tree to await our pleasure," and the maharajah was instantly seized by three or four powerful Arabs, and secured to a tree some twenty paces away.

"What about his valuables, sir?" asked Carl.

"Have you examined them?"

"Yes, sir."

"And what do they consist of?" asked the king.

"His jewels, his gold and silver plate, studded with rare gems of priceless value. They are worth five times the value of the specie," whispered Carl.

"And what else? You said there were ten boxes."

"Part of his regalia and numerous ceremonial robes."

"They are all confiscated!" announced the monarch. "The sun will set in another two hours, and at sunset the Indian must die."

"There is nothing else, sir, of much value. All the gold and this personal property has been secured. Here is the list of passengers, for there are scarcely any passports held by the strangers," and here Carl, who had paid a visit to the aerial, whispered something to his chief.

"Good! Then, in your opinion, chancellor, sufficient tribute has now been obtained from these strangers who have crossed our territory without permission," said the bandit aloud for all to hear.

"Yes, sir."

"Then let them board the airship at once. She will be cast adrift in ten minutes."

At this there was a scramble for the gondolas, and very quickly all, save the captain and the navigating officer, were aboard. The judge and the colonel, however, prevailed upon by the maharajah’s men, descended again to intercede for the life of the Indian.

"You have taken the man’s jewels," said the colonel. "At least you might spare his life."

"You may have his body," remarked the airman, "but he must first drink the phial," and a stern look appeared once more in the robber-bandit’s eyes. On this point he was unbending, and remained like adamant.

"The airship is ready now, sir," said the captain, making a final appeal for the life of the maharajah. "I should like to report, at any rate, when I do complete my journey, that all my passengers are safe, though I expect to be two days late with only two engines and this beam wind. Once more, will you release the Indian?"

"Bring him before me!" commanded the monarch at last, with a bored expression, and the Indian, still bound hand and foot, was brought before the pseudo king.

"Unloose his hands," came the order.

"They ask me to spare your life, Indian dog!" continued the robber, addressing the prince in contemptuous tones. "If you sue for it yourself, you may have it, otherwise..." and, instead of completing his sentence, the speaker shook the little phial in the face of the prisoner.

"I will not ask my life of you, serpent!" hissed the captive. "From you I will accept no favours. Robbed of my family heirlooms, my jewels and my household gods, I prefer to die. Give me the poison, and I will show you how a real prince of the royal line of Indus can die!"

For one awful instant, the desert chief glared at his enemy, who had dared to refuse his generous offer. Then, in angry tones, he cried:--

"Indian dog! I offered you mercy, but you spurn the gift of Allah and ask for death. Then take this and drink it!" and he tossed him the phial.

"Stay!" cried half a dozen voices from amongst the group of passengers.

But their expostulations were in vain, for, with an eagerness to hide his disgrace in death, which only a proud oriental can show, the prisoner caught the phial, withdrew the small cork, and drained the contents before his horrified friends could interfere.

The next moment, the body of the maharajah lay prostrate upon the sands of the Hamadian desert.

*CHAPTER XIII*

*THE MISSING AIRSHIP*

Horrified and aghast at the foul deed which had been done, the passengers and crew of the air-liner, who had left the gondolas at the cry of consternation which went up, now crowded around the fallen prince. Even those fierce sons of the desert who witnessed the dire act could not restrain an involuntary shudder, but they merely shrugged their shoulders, or remarked: "Kismet! It is the will of Allah, the Compassionate, the Merciful," and after some such invocation, their piety appeared to be satisfied, for they immediately returned to their treasure.

The captain and his friends were loud in their protestations and imprecations after their first and futile attempts to rouse the prostrate man, for they believed him to be already dead. They glared at the pseudo caliph, who appeared to be entirely unmoved by the heart-rending spectacle. And if, at that moment, any weapon of offence had remained in their possession, it would certainly have been turned upon the offender, whom they now regarded as a murderer.

But every weapon had been carefully removed from the air-liner and her complement; even the unmounted machine-gun and the one box of ammunition placed aboard on her first voyage, were now in possession of the bandits.

The captain in particular was furious, and he turned upon the German fiercely, shook his fist at him and cried, "One day you will pay for this, sirrah! The arm of Britain is long enough to reach you!"

A mocking laugh was the only reply which the German gave. Then, looking once more at his jewelled watch, he signified that the time for the airship’s departure had almost arrived.

"Three minutes more and I shall cut her adrift," he said.

"But the maharajah?" asked the captain. "What can we do with him; we cannot leave his body to the vultures."

"Bah! Take him away with you. He will live again in seven hours; it was only morphine!"

Bewildered, but yet relieved by these words, they quickly ascertained that the prostrate man was not actually dead, and they hurriedly placed him aboard the airship and administered emetics.

"Let us get him away at once," urged the Indian judge; "perhaps the higher altitudes will quickly dissipate the effects of the morphine."

"Are you ready there?" shouted the caliph, who had ridden with his escort up to the central gondola.

"Yes," came the response.

"Then remember, the next time that you invade my dominions without my permission you will not escape so easily. As you know to your cost, the King of the Hamadian desert is able to defend himself and his people, even from the insults of a great power."

The captain made a slight bow, half ironical, in response to this kingly assertion, and asked,

"Is there any communication which your majesty would like to have delivered to my Government?"

"Yes," replied the monarch, drawing from under his loose robe a sealed packet, which he appeared to have had in readiness for the occasion. It was addressed as follows:--

"To Colonel John Tempest, D.S.O., M.C.. Chief Commissioner of the British Aerial Police, Scotland Yard, London,"

and across the top left-hand corner it was marked "_Confidential_," and also "_To be delivered personally by the Captain of the Air-Liner, Empress of Britain_."

The skipper, apparently bewildered for a moment by this strange request, for it seemed to him like a letter from a condemned man to his executioner, looked the packet over for a few seconds. Noting the great red seal on the back, he read the imprint embossed on the huge wafer. It read as follows, and was circular in form:--

"From Sultan von Selim, Air-King of the Hamadian desert," and the crest was a scorpion, with the solitary word in Latin, "_Scorpio_."

The caliph waited patiently until the captain had examined the exterior of the packet, and recovered from his amazement, and then said, "Before you depart, Captain, you must promise me that you will deliver that packet in person to Colonel Tempest, who is not unknown to me."

The captain did not answer for a few seconds, for he was wondering what new conspiracy was this. He was wondering also whether the conveyance of this packet was not after all the real reason for the forced descent of the airship.

"Do you promise, Captain?" asked his interrogator, looking at him fixedly.

"Yes, I promise."

"On your honour?"

"On my word of honour, I promise to deliver it."

"Then good-bye. I will ’wireless’ the patrols to look out for you."

"Thank you," replied the skipper acidly.

And the next moment, seeing that only his own accomplices and reputed subjects were left on the ground, the Sultan gave the order, "Let go!"

So the huge cable was slipped, and the leviathan left her moorings at once. The north-west wind carried her clear of the trees, and, as she had left nearly two tons of her most precious cargo behind, she rose rapidly, then started falteringly on her long journey to Cairo as her two remaining Sunbeam-Maori engines burst into life.

The sun, which had shone with pitiless might upon the Arabian desert that day, was sinking like a huge red ball beneath the horizon when the great air-liner, drifting considerably from her course, but still making progress in her journey towards Cairo, disappeared from the watchers’ view.

With strange impartiality, inexplicable in such a robber-bandit, the spoil had been divided amongst the Bedouins, who, to their bewilderment and surprise, were now rich, each one of them, beyond the dreams of avarice. Their gratitude to Allah, the Giver of all Good, and to the great white sheik was unbounded. Never before had their greedy eyes beheld such treasure; never before had they gained a prize so easily; and some of them even wondered whether, after all, Mohammed had not appeared to the Faithful once more in the person of the great white sheik.

Long before midnight, however, the last man, with heavily-laden beast of burden, had disappeared, swallowed up, as it were, by the very sands of the desert, so that, when the full round moon approached the meridian and changed the gold of the desert to silver, not a vestige of man or beast remained. And of the camp, only a few ashes marked the spot where once a fire had burned. The _Scorpion_, too, had taken its departure for an unknown destination, carrying its mysterious crew far, far away from these burning sands, for the indomitable commander knew only too well that the captain spoke truthfully when he said that the arm of Britain was very long, and could even reach to this wild desert land.

Before his departure, however, Heinrich von Spitzer had sent off his promised message in laconic terms to the Cairo patrols. It ran as follows:--

"Air-liner _Empress_ with damaged engines crossing desert towards Cairo. Lat. 29-50 N., Long. 40-25 E. drifting W.S.W. Wireless deranged. SCORPIO."

"Piece of bad luck, sir!" remarked the commissioner’s assistant at Cairo when he received the message.

"H’m! She carries the Indian mail, too," replied his chief.

"Yes, and a good deal more, sir."

"What else does she carry this trip besides passengers and mails?" asked the alert commissioner.

"That big loading of specie, sir, for the Bank of England. Nearly a ton of gold, I believe."

"Phew! And isn’t the maharajah of somewhere or other coming on a state visit to the King also?"

"Yes, by Jove, so he is! We had a message this morning saying that he would travel by the _Empress_."

"Heaven help us if she comes down in the desert with that cargo. The Bedouins would soon make short work of it. The authorities rely too much upon the patrols for these long journeys," said the commissioner.

"We were asked to take particular care over her this trip. The Delhi patrols accompanied her part of the way, and she was all right up to mid-day, but she hasn’t spoken to us since. I have sent out one or two messages and have had the patrols ready to go out and meet her, as soon as I heard again from her, giving her position, sir."

"And you’ve had no further reply till this message came in?" asked the chief.

"No, sir."

"By the way, is her wireless damaged as well as her engine? I didn’t notice."

"Yes, sir. The message says: ’Wireless deranged,’" replied the assistant, re-reading from the aerogram.

"Then who the deuce sent the message?"

"Scorpio---- But who Scorpio is I can’t make out. It must have been some passing airman, for it cannot have been one of our own patrols."

"Phew! The mystery deepens. Get the patrols out at once, and tell them to take plenty of ammunition with them. It will take a few rounds to scare off those Bedouin fiends if once they get round a carcase where there are such pickings."

"I don’t think there’s much to worry about in that respect. Those Arabs have a wholesome fear of these air-liners, sir. However, I will get the machines off at once."

*CHAPTER XIV*

*BETRAYED BY THE CAMERA*

The order was quickly given for the aerial police scouts to start. Within a few minutes the patrols left Cairo and the adjoining air-stations, and, spreading out fan-wise, they crossed the Canal, the Gulf of Sinai, the wild mountainous peninsula which bears the same name, and the Hedjaz coast, until they entered the desert regions beyond. Then they commenced their search by moonlight for the battered and drifting air-liner over the trackless, desert lands which lie between the 28th and the 30th parallels.

By a pre-arranged system of Very lights, the patrols kept each other informed of their exact positions during the night, and watched keenly the eastern horizon for any response which might come from the belated airship.

Meanwhile the air-liner, fighting manfully against the freshening wind, made very slow progress, and drifted still further and further away from her course. The air was full of wireless messages both from Cairo and the patrols, but she was as yet unable to reply and define her position. The engineer and wireless operator, however, had been able to receive some of the messages indistinctly, and they knew at any rate that help was not far away.

The captain was naturally very much depressed by the turn of events. Somehow he felt that he had not acted very heroically in the matter. He had considered the safety of his distinguished passengers perhaps too much.

"If I had had no passengers to consider, I would have remained aloft until the whole liner had been shot to ribbons!" he declared to himself, when he at last retired for a few minutes to his private cabin. "They should never have taken me alive! But there, my instructions stand--the safety of the passengers and crew before anything else. I was a fool, though, to act as I did. I ought to have sent out the S.O.S. to Cairo without a second’s delay, instead of arguing with this brigand; but there, whoever expected to encounter anything like this?"

Then as his thoughts turned to the wonderful machine, he endeavoured to docket all the information he could remember about the brigand’s aeroplane, for he knew that he would be expected to recount every detail when he met the court of enquiry, "which," he murmured, "is as certain to take place as to-morrow’s sunrise.

"Gee whiz! Three hundred miles an hour, and silent engines to boot! Phew! nobody will believe me, anyhow. Still, I shall have to face the music, and also to explain why I have lost a hundred thousand pounds of specie," and the skipper looked down on the white sands below, and for a moment he almost contemplated suicide.

"I wouldn’t mind if I could only bring sufficient information to the authorities to lead to the speedy capture of the villain, but I can’t. There wasn’t time even for a photograph. The bandit was aware of all that, and I understand that every camera was removed from the airship before he let us go."

At that instant there came a slight tap at the cabin door.

"Come in!" cried the commander, expecting some further report from the sick-berth steward about the condition of the maharajah, who, half an hour ago, was said to be showing signs of recovery, owing to the bracing air at three thousand feet.

The door opened, and Gadget, the ship’s mascot, appeared. Now Gadget’s newest hobby was photography, and through the kindness of the photographic officer he had become the proud possessor of a small pocket camera.

"I got her, sir! Thought you’d like to see her ... begging your pardon," and Gadget, with his dirty, but sunny, smiling face stopped short and pulled his lock of hair by way of salute, as the captain pulled him up sharply by snapping out:--

"Got whom? Like to see whom, Gadget?"

"The ’Clutchin’ Hand,’ sir," explained Gadget, who now found himself floored for once by his want of English.

"I don’t understand, boy?"

"The bloke what played the dirty on us, sir," replied the boy, opening wide his bright blue eyes, and holding out three wet and recently developed pocket films.

"Him what got the swag, sir," continued the urchin, endeavouring to make himself clear.

"Oh, you mean that you photographed the brigand!" replied the skipper as he caught sight of the negatives, and snatched at them eagerly, a new light coming into his eyes.

"Yessir!" exclaimed the lad. "Him what said he was a King of the Desert."

"Gadget!" exclaimed the captain, after a brief examination of the films, which were really three fine, clearly defined pictures of the _Scorpion_, showing her in mid-air, when alongside the _Empress_.

"Yessir," replied the excited youth, not yet certain whether he was going to be hanged or praised for his offence.

"You have shown more wit and skill than anyone on board the airship. You shall be well rewarded for this, I promise you. How on earth you managed to get three good snapshots like these, all showing different angles of the machine, and to hide them away, is beyond me!"

"Thank you, sir! Thought you’d like ’em," and the boy’s eyes sparkled even more than ever as the captain shook him by the hand, and planted five new, crisp Bradburys therein, then dismissed him.

"Great Scott!" exclaimed the captain, "but that little urchin’s saved my reputation. These photographs may prove of more value to the authorities than the lost treasure. I feel a different man. Here is extraordinary evidence against the culprit. One photograph shows the fiend actually firing a burst at the twin engines in the rear gondola, and another the faces of the two occupants above the fuselage. They will show more evidence still when they have been enlarged." And the captain, after carefully drying them, placed them in an envelope and put them into his inner coat pocket, muttering:--

"Smart little beggar! I wish I hadn’t punished him the other day for smuggling that tobacco aboard."

The captain, who had left strict instructions that he should be called half an hour before the end of the watch, in order that he might relieve the navigating officer, was just about to lie down on the couch for a brief spell, when suddenly another knock at his cabin door startled him, and immediately after his servant entered and announced: "Seven bells, sir."

"Already?" exclaimed the captain.

"Yes, sir."

"Has the moon set, yet?"

"Yes, it is quite dark now, sir."

"All right. Tell the navigating officer that I’ll be down in one moment."

At this very instant the telephone bell which connected the cabin with the navigating gondola rang furiously. Snatching up the receiver, the captain asked, "What’s the matter, Donaldson? Is there another raider on the starboard bow?"

"No, sir, but there’s something very much like a signal flash away in the north-west."

"Sure it wasn’t a shooting star?"

"More like a Very light, sir, but very faint," replied the navigating officer. "Shall I reply, sir?"

"Yes, give him three red lights. I expect it’s one of the patrols looking for us. I’m coming down now," and the captain replaced the receiver, and made haste down the corridor which led to the chart and navigation room.

The next instant three red balls of fire fell from the airship earthwards in rapid succession, and within a couple of minutes a faint gleam of greenish light fell like an arc in the north-western sky.

"Yes, the patrols have found us, sure enough," exclaimed the captain, who had now joined the officer.

After several further exchanges of fire-balls, repeated now from two or three quarters, the searchers closed in upon the straggler. Then a rapid dialogue took place by means of the morse lamp, and, when dawn came, shortly afterwards, no less than six fighting scouts, running at about a quarter throttle, surrounded the wounded leviathan, and escorted her towards Cairo.

When the _Empress_ reached that town, she was already twenty-four hours overdue at London, so the cables and the wireless stations were busy with messages relating to the missing liner, and with more than one inquiry as to the safety of her cargo, evidently from the consignees, or more likely still, from the underwriters.

And when the captain told his story to the Commissioner of Aerial Police at Cairo there was another mighty stir, and both the cables and the wireless were busy again, for the whole civilized world was tingling with excitement to know something tangible about this man of mystery--the phantom airman. And the story of Gadget’s photographs was told to the world.

*CHAPTER XV*

*DIAMOND CUT DIAMOND*

While the events recorded in the last few chapters were taking place, a series of adventures not less exciting and perilous had befallen the two airmen, Keane and Sharpe, in their endeavours to track that ingenious conspirator, Professor Rudolf Weissmann, in his secret retreat within the dark recesses of the Schwarzwald.

After their midnight consultation with Colonel Tempest at Scotland Yard, their instructions were to proceed early next day, by whatever aircraft was then available, to Germany, and once there to adopt some suitable disguise, and institute forthwith a most rigorous search for the secret aerodrome. They were to leave no stone unturned in their efforts to track down this great German irreconcilable, who had dared to hold a pistol at the civilized world, and to bring back, if possible, some tangible clue concerning his two great discoveries.

"Time is short," the colonel said. "Immediate action on our part is vital. Spare no expense in the venture, and if necessary you must even proceed to extreme measures to capture this daring outlaw and his accomplices."

"And what about this phantom aeroplane?" asked Keane. "Apparently it has already left the Schwarzwald on its piratical expedition."

"It may return, and you must watch for it. Some of those scattered inhabitants of the Black Forest are sure to have seen or heard something of it. Its trial trips must have been carried out somewhere in the vicinity."

"They are a simple and primitive type of people who still inhabit those forest wastes; wood cutters, lumbermen, makers of little wooden clocks and musical boxes, most of them, I believe," added Sharpe, who had often traversed those regions as a British spy during the Great War.

"Then they should be easier to handle," added the commissioner of aerial police, who had a ready method of brushing away apparent difficulties. "I am compelled to rely almost entirely upon your efforts. Take your pocket-wireless telephones with you and a sufficient quantity of German gold and silver, and start directly you have had a few hours’ rest."

"We will get away immediately after breakfast, sir," replied Keane, who had already made up his mind as to how he should proceed in the matter, for he had fixed up his jumping-off ground for the Schwarzwald, and also the type of disguise he intended to adopt.

"Good-bye, both of you, and may good fortune attend you!" said the colonel.

"Good-bye, sir."

Big Ben was striking three o’clock as they left Scotland Yard and made for their quarters, which were in that part of London known as The Adelphi, a quaint, old-fashioned ensemble of buildings of the Georgian period, overlooking the Thames, not far from the Watergate. A few minutes later they bade each other good-night, and turned in for a few hours’ sleep before their long flight across England and France.

At seven o’clock they were breakfasting together in a private room overlooking the river, and discussing the details of their coming adventure.

"The Schwarzwald!" Sharpe was saying, as he helped himself to another egg and a rasher of ham. "Where do you think, now, we had better start from, Captain Keane?"

"Mulhausen," replied the other promptly, for with Keane the initial procedure was already cut and dried.

"Mulhausen? Capital! I was thinking of Strasburg, but your idea is better still. Is there a good aerodrome there where we can land?"

"Yes, on the banks of the little river Ill, which runs into the Rhine a little lower down. And once across the Rhine we are already in the Black Forest, though we shall still have a long tramp to the place which I suspect," added Keane, pouring out another cup of coffee.

"Oh, yes, I remember the place; the aerodrome is near the junction of the Rhine-Rhone Canal," replied his companion.

"You’ve got it, exactly. Now we must get away; it must already be seven o’clock, and a fine morning to boot. What says the weather report about the Channel crossing?"

"Here it is," exclaimed Sharpe, passing a copy of the _Times_ across to his friend, who turned over the pages and read as follows:--

"Flying prospects for to-day:--South-east England and Continent, including the Channel crossing, favourable for flying for all types of machines till mid-day, after that conditions will deteriorate, squalls and heavy rains will predominate, visibility will be poor, and conditions will become unsuitable for cross-country flying."

"Good! Then we must get away at once," observed Sharpe, and within another five minutes they were being hurled along towards Hounslow, the aerodrome from which this new adventure was to begin.

Forty-five minutes later a couple of S.E.9s, the fastest machines in the service, rose from the flying ground and steered a course east-south-east for the Straits of Dover. Thirty-five minutes later, the necessary signals having been accepted by the Dover patrols, with throttles wide open, the two daring young aviators rushed the Channel at one hundred and fifty miles an hour.

The French patrols having been informed by Dover, permitted them to pass unchallenged. And now changing course till they steered almost due south-east, they sped onwards, catching now and again a glimpse of the old battle-front of the days of 1914-1918, where the shell-marked craters of the Hindenberg line were still visible from the air.

Then they followed the railway line from Laon to Rheims, left the ancient town of Nancy to their left, and, crossing the Vosges Mountains and forests a little to the north of Belfort, they dropped down quietly to the landing ground outside Mulhausen in Alsace, as the clock in the Market Square struck the hour of noon.

Having left their machines and flying gear in charge of the commandant, they entered the town, purchased a portable camp outfit, and, dressed as tourists of the pedestrian and naturalist type, continued their journey, crossed the Rhine and entered the Schwarzwald, ostensibly to study the fauna and flora of the Black Forest.

"Phew! I’m tired of this load. Let us camp here for the night, by this little clearing, where these seldom trodden footpaths diverge," said Keane, some hours later, as, weary and dusty with his three hours’ tramp through the bracken and the tousled undergrowth, he threw down his heavy knapsack and nets, and began to wipe the perspiration from his forehead.

Then they lit a small fire of dried twigs, cooked their evening meal, and lit their pipes.

After a quiet smoke, during which time they carefully re-examined a survey map of the Schwarzwald, they began to talk in low whispers, whilst the sun descended amongst the pines on the western heights, over which they had dragged their weary feet.

"It is my opinion," whispered Keane, "that we are within five miles of that secret aerodrome."

His companion nodded, almost drowsily, although every faculty was kept constantly alert.

"It is just possible that one of these paths leads to the very spot, but it will be necessary to explore them both. We must be extremely careful, however, for this professor is sure to prove a wily opponent. I hope, however, some wood-cutter or peasant may pass this way soon, and that we may learn something from him which will help us," continued the senior airman.

"What if the wood-cutter should prove to be the professor himself?" asked Sharpe, with a humorous twinkle in his eyes.

"It is even possible," returned his companion.

"In that case it would be diamond cut diamond, Keane, eh?"

The other shrugged his shoulder at the very thought, and prayed that such a contingency might not happen, at any rate until something tangible had first been discovered.

"In three hours it will be midnight," he said. "If no one passes this way by then, I think we must carry out our search in the dark. Time is pressing; we must find something within another forty-eight hours, or poor old Tempest will be at his wit’s end, and calling us home again. He cannot leave us long on this trail."

"The greater the pity. A fortnight is not too long to follow a trail like this," said Sharpe.

"Yet you had to do things pretty smartly in those dark days of 1917 and 1918, Sharpe."

"Yes, and there was some danger and excitement attached to it, which sharpened one’s wits."

"Never fear! There’ll be both before we have finished this trek," returned Keane.

"Hist! What was that?" said Sharpe in an undertone, as he caught the sound of broken twigs.

"Someone approaching," whispered his companion.

They listened acutely now, with every sense keenly alert. Again they heard the sound, and it seemed to come from the western side of the open glade, where the last dull glow of the sunset still revealed the edge of the forest.

The camp fire had died down to a smoulder, but Keane instinctively held his ground sheet before the dying embers, lest their presence should be betrayed. He was anxious to learn something of the nature of this visitor before he revealed himself.

"Bah! It is some creature of the forest," observed Sharpe, after a moment’s hesitation. "A wild boar or a red-spotted deer, most likely."

He was right, for the next moment a series of grunts proceeded from the spot whence came the sounds, and, as though suddenly startled by the consciousness of some human presence, the beast, a fine specimen of the _Sus Scrofa_, with fierce protruding tusks and long stiff bristles, broke cover, trotted swiftly across the glade, within thirty yards of the two watchers, and entered the forest on the other side.

"So much for that little incident," muttered Sharpe, as he released his grip of the Webley pistol, which his right hand had instinctively grasped, when the dark shadow broke from the margin of the trees.

Keane shook his head as though he disagreed with his companion, and remarked in a low voice, "The creature was evidently startled or it would not have fled like that. Its scent is very keen, and as the wind is blowing from the west, it suspected danger from that quarter."

*CHAPTER XVI*

*THE GHOSTLY VISITANT*

A few moments later the two men were startled by the sound of a human voice, trolling out the words of some German folk-song, and approaching from the same quarter towards the clearing.

"This is our man," exclaimed Keane, as he removed the screen from the fire and stirred the dying embers into a cheerful blaze, piling on more dried twigs, so that the trees about the glade seemed to dance like fairies.

"Some woodman or peasant returning from a party," observed Sharpe.

"I wonder where his cottage is," replied his friend; "it must be somewhere in the neighbourhood."

"We must welcome him to a belated supper. Perhaps this good Rhine wine will open his lips still more, and he may tell us something about the birds of the Schwarzwald."

"Particularly the phantom-bird," facetiously observed Keane with a smile.

Nearer and nearer came the stranger, breaking occasionally into snatches of song, as though he would frighten away the goblins and weird creatures of the forest, for of the superstitious peoples of Europe, the peasantry of the Black Forest are most given to credulous beliefs. Perhaps this is because no other district of Europe is so rich in quaint legend, folklore and ghostly tradition.

Now and then the approaching stranger would stop his singing to address some remark to a companion; evidently some beast of burden trudging beside him. The next moment the figure of a man, leading a pack-horse through the forest, suddenly emerged upon the clearing. Catching a sight of the dancing flames which mounted skyward as one of the airmen stirred the fire into life, and beholding the dark figures of the two strangers, the newcomer, suddenly stopped, apparently half-terrified by the sudden apparition.

"Geistlich!" he muttered, staring with wide-open eyes towards the sudden flame.

"Guten abend, freund!" exclaimed Keane, wishing to draw the man into conversation.

The man’s fears departed as soon as he discovered that he was addressed by human beings like himself, for in his first wild flight of fancy he feared it was far otherwise, and that he had suddenly come upon one of those forbidden glades, where the sprites and goblins dance after dark.

"Guten abend!" he replied, and, being asked to join the company, made haste to do so, reining in his loaded horse and tethering him to a tree-stump close by.

"’Tis late to travel these lonely woods, friend," said Keane in excellent German.

"Yes, ’tis late, but the moon will soon be up, and then, why, ’twill be better footing," replied the stranger, whose full, round face and longing eyes were already directed towards a wicker-covered bottle, which seemed to hold something good, so that he smacked his lips once or twice, and in fancy he was already draining the sweet nectar which the bottle contained.

"Have you far to go?" asked Sharpe.

"Why, yes, ’tis another seven miles to my cottage in the woods."

"Then stay with us an hour until the moon shall rise and clear away the goblins of the Schwarzwald," urged Keane, who, by this time, had been able to examine the stranger’s face by the light of the fire, and to read it like a book.

"A simple, credulous fellow, a true peasant of the Schwarzwald, untouched by the outer world," he told himself. "He should be useful to us." Then, passing to him the wicker-covered bottle, he said:--

"Good Rhine wine from Bacharach, Hans. Taste it!"

"Ach, from Bacharach on the Rhine, Comes the finest sort of wine,"

exclaimed the stranger in the rude dialect of the Black Forest, and his round eyes sparkled as he clutched the bottle, raised it to his lips, and drank half a pint without stopping to take breath.

"’Tis a long time since I tasted such rich and luscious wine, gentlemen," said the peasant, handing back the bottle.

"Pray be seated and rest awhile," urged his companions, and nothing loath to keep such excellent company, Hans, if such was really his name, sat down by the fire.

"Pray, what brings you to the lonely Schwarzwald, gentlemen? Have you come to hunt for the wild boar, or to fish the mountain streams?" he asked, "for I can show you where the biggest fish are to be found, and where the wild pig rears her litters."

"Butterflies and birds, especially birds," replied Keane, pointing to his nets, and his neat little boxes for packing specimens.

"Birds? Ach, there is one bird which sometimes flies in these parts which you will never catch," said the peasant, speaking in lowered tones, as though half-frightened by his own words.

"Ha! What bird is that?" asked the others.

"Hist!" exclaimed Hans, raising his forefinger, and looking guardedly around. "It is the phantom-bird!"

"The phantom-bird?" echoed the two airmen, who could scarcely believe their eyes and ears, as they earnestly regarded this solemn, frightened, half-childish man, who had evidently seen the very thing they had come so far to find, but who believed it to be something supernatural.

The two Englishmen glanced at each other. Had they really found someone who could enlighten them about this mysterious aeroplane, for he could certainly be referring to nothing else? And at that moment Keane blessed his lucky star, which had led him to choose these wild forest regions for their jumping-off ground. Still, they must not appear too curious, lest they should betray the reason of their presence here.

Keane shook his head as, with an apparently incredulous laugh, and a sympathetic motion of the hand, he would banish all tales of ghostly visitants to the realm of limbo. This only had the effect of egging on the speaker to tell his tale, however.

"Ach, Himmel!" he exclaimed. "Es war geistlich!"

"Did you see it, then?"

"Ya, das hab ich!" returned the other.

"Was it in the day or the night-time when you saw it?" asked Sharpe.

"It was night, about this time, and there was but a half-moon above the tree tops."

"Were you very much frightened, Hans?"

"Yes, I was scared to death almost. I thought the old man of the mountains had come for me. I had been to market to sell my little wooden-clocks, and near this very place the huge grey phantom bird swooped down, then circled round and round and disappeared there, over there!" and the peasant, his eyes almost starting out of his head with terror, pointed away to the east.

"Bah! It was no bird, it was an aeroplane, Hans. You should not have been frightened," exclaimed Keane, who had been taking particular note of the direction in which the mysterious machine had disappeared.

"Yes, a ghost-aeroplane!" iterated the Schwarzwalder. "There has never been anything like it before."

"Did anybody else see it?" queried Sharpe, passing the bottle once again to Hans, who stayed but a moment to wipe his lips with his sleeve, and to take another deep drink of the wine.

"Ja, it was seen by Jacob Stendahl the same night, not far from this very place."

"And who is Jacob Stendahl?" asked Keane.

"He is the woodcutter whose cottage is down by the stream, two miles away. That path leads to his house. He was terrified; he said it was an evil omen, and next morning his little Gretchen died."

"And what happened to you, Hans?" asked Sharpe.

"That same night my sow farrowed, and all the litter were dead next morning," replied the peasant gravely.

A deep silence followed this last remark, and the Schwarzwalder brooded over his misfortune, and lamented to himself the loss of his fine litter of young pigs.

The two airmen felt certain now that Hans had really seen the mysterious aeroplane, and they plied him with a dozen further questions as to the noise it made in passing, and the speed at which it travelled, and whether anyone else had seen or heard of it. To some of their questions Hans could give no coherent answer. He said, however, that very few people lived in this part of the forest, and parts of it were seldom or never trodden by human foot. He had spoken to one or two about it, and they also had either seen or heard of it from someone else, and the general opinion amongst the Schwarzwalders in that part, was, that it was one of the dead German airmen, whose spirit came to visit the spot in a ghost-aeroplane.

"Which of the German aces is it, then, that revisits this place, do they think?" asked Keane.

"Some say that it is the ghost of Immelmann, who used to come here before the war to hunt the wild boar; others say that it is the spirit of Richthofen, but I cannot say," replied Hans.

On the question of speed and noise, however, the peasant declared that he was certain.

"It must have been a ghost-aeroplane," he said, "because it was silent, and its speed was like the passing of a spirit when it leaves the body."

A deep silence followed these words, but at the end of a few minutes Hans, pointing to the east, said:--

"Look, friends, the moon is rising already. It is getting lighter, and I must go."

Then, untethering his pack-horse, he thanked the strangers for their hospitality, gave them the direction and situation of his cottage, where they would be welcome, should they care to visit him during their stay in the Schwarzwald, and, bidding them adieu, started off on his journey through the forest.

*CHAPTER XVII*

*THE WATCHERS*

They watched the Schwarzwalder and his beast of burden disappear into the forest, then for some minutes the two Englishmen, buried in thought, sat by the embers of the fire. Neither spake to his companion for a while, as, deep in contemplation, each endeavoured to fathom in his own mind this secret of the phantom aeroplane, this riddle of the sphinx. At last Keane addressed his colleague.

"This travelling clock-maker has confirmed our theory, Sharpe," he said.

"Yes, the simple fellow has helped us not a little," replied the other.

"We must continue our search without further delay, lest this talkative peasant should himself encounter this genius, and unwittingly announce the presence of two strangers in the forest. That is my great fear now."

"You don’t think this fellow misled us, Keane?"

"Why do you ask? He was too dull-witted to be anything in the nature of an accomplice," replied the captain.

"Quite so, but he might have been a tool in the hands of this mystery man," added Sharpe, as a sudden feeling of suspicion shot across his mind.

"In that case we ought to have followed him, but I scarcely think it worth while. A dull-witted man of that type would have been too dangerous to his employer, even when used merely as a tool. The only danger I anticipate from that quarter, unless I am utterly mistaken, is that the fellow may encounter someone in the forest who is engaged in the plot, and thus reveal our presence, as I stated previously," observed Keane, as he began to get his traps together, ready for the march.

"Anyhow, we have learned something from the Schwarzwalder."

"By the way, Sharpe, you might tune up your little wireless pocket ’phone, and ascertain if there are any messages floating around."

"So I will; we might pick up something," replied the junior airman, and the next moment he climbed into a straggling, low-branched tree, uncoiled a small aerial, and, starting his little battery, listened attentively for any stray message that might be floating through the ether.

"Anything?" asked Keane, coming to the foot of the tree.

"Nothing," remarked the other.

"Then we’ll push off."

Five minutes later, having adjusted their packs, collected their nets, and having stamped out the remains of the fire, they were ready to start.

"Which path shall we take?" asked Sharpe, for there were two ill-defined, grass-grown tracks which led away from the clearing. One led past Jacob Stendahl’s cottage, and had been followed by the Schwarzwalder, and the other, the lesser trodden of the two, led they knew not where.

"Let us take the one on the right," said Keane, indicating the latter. "It is more likely to yield us something," and the next moment they were hidden from sight amid the dense undergrowth of this part of the forest.

Scarcely had they disappeared from view when one of the upper branches of a tree near to the edge of the clearing suddenly appeared to move, then to swing loosely for a second, and drop to the ground. Then for a moment there was silence, save for the call of a nightjar which had been disturbed, but a moment later a dark shadow debouched from the edge of the forest and crossed quietly but quickly to where the fire had been burning a few minutes previously.

A low whistle, repeated twice, brought a similar shadow from the opposite side of the clearing, and the two indistinct, but human shapes, met each other face to face.

"Who were they, Professor?" asked the second arrival of the first.

"Himmel! Ich weiss nicht, Strauss," replied his companion, who was none other than the renowned Professor Rudolf Weissmann, "but I fear that they portend us no good."

"Let us examine the ground to see if they have left any clue behind."

So for the next few minutes the professor and his mechanic searched the ground carefully for any little souvenir which the travellers might have left behind them. And whilst they searched, they talked in low, but eager whispers.

"Did you hear that half-witted Schwarzwalder talking aloud about the _Scorpion_?" asked the professor.

"Yes. He called it a phantom-bird, did he not?" replied Strauss. "I heard nearly all he said, he spoke so loudly and coarsely."

"Could you hear what the others said?"

"Not a word; they spoke so quietly, save once or twice when they spoke to the clock-maker."

"Nor could I, and that is what makes me so suspicious," returned Weissmann.

"They spoke good German, though," ventured the mechanic.

"Bah! Of course they would. Nevertheless, it’s my firm opinion that they’re foreigners, and that they’re here for some special reason."

"And that reason is?"

"To find out about the _Scorpion_," snarled the mathematician.

"Ach!" exclaimed the other; "the _Scorpion_ is two thousand miles away."

"Then their next business is to find the aerodrome," said the professor.

"Blitz! that they’ll never do except by accident. Think of those live wires waiting for them if they get within a hundred yards of it. We have found six dead men there already; I don’t want to dig any more graves," returned Strauss.

They had continued the search for fully ten minutes, and the professor, occasionally flashing his pocket torch, was carefully examining the long grass within a radius of some twelve of fifteen feet of the spot where the fire had been. Wise man that he was, he carried out his final investigation to the leeward of the fire, trusting that the breeze might have carried some paper fragment, used in lighting a pipe or starting the fire, in that direction. Nor was he disappointed. He was just about to conclude his search, however, when his sharp eyes caught sight of a piece of half burnt and twisted paper hidden away amongst the longer grass.

"Donnerwetter!" he exclaimed under his breath, as he flashed his torch upon the paper for a second. "I thought so; here is evidence enough for an execution."

"What is it, mein herr?" asked the mechanic, hastening to his side.

"Do you see that?" said his companion, untwisting the paper once again and flashing a light upon it.

"Ja! ja!" replied the other as he strained his eyes in the attempt to decipher the handwriting on the half-burnt sheet. "But I cannot understand it, for it is in a foreign language."

"It is part of a small fragment of an envelope, and the writing, which is in English, is certainly almost undecipherable, but I can distinguish the letters ’...eane’."

"Ach, Himmel! That is Keane!" replied Strauss. "He is one of the aerial police, is he not?"

"You are right, Fritz. This letter was addressed through the English post to Captain Keane, one of Tempest’s best men, if not indeed his most brilliant ’brain-wave,’" hissed the professor.

"Donner und blitzen! Then he has come here to search for the _Scorpion_, and the aerodrome."

"Yes, but look, he only left London a few hours ago, for here is the London postmark in the corner, bearing yesterday’s date."

"And his companion? Who is he?" asked the mechanic.

"It must be that other scout pilot, Sharpe; they work together. But, mark my word, Friedrich Strauss, they are mistaken if they think to find an easy victim in Professor Rudolf Weissmann. I’ll teach them to track me like a murderer through the Schwarzwald. They have come to the Black Forest, and here they shall stay." And for once, the quiet, mild-mannered professor jerked out his words with unusual vehemence.

The mechanic saw that his chief was deeply agitated by this sudden discovery, which confirmed all his recent fears, and to allay his feelings, he said,

"But they will never find the aerodrome, Professor, or, if indeed they find it, they will never enter it alive; think of the preparations you have made for all uninvited guests," and the speaker shuddered, for he knew something of the terrors of that "death-circle" in the lonely forest.

"Bah! it is my secret they want, the secret of that mysterious power which drives the _Scorpion_."

"Uranis?" ventured the other.

The professor nodded, for he regarded it as the greater success of the two. Without it the _Scorpion_ would be useless; with it a dozen _Scorpions_ could be built, once the facilities were provided. Unfortunately the discovery had been effected too late to win the war for the Fatherland. Besides, he had not received the encouragement from the government that he had deserved, and his soul was consequently embittered.

"Come," he said at last, "we must get back to the aerodrome and watch for these half-witted Englishmen. Once there we can afford to laugh at them. They will soon be held in a vice. But I must send a further message to the _Scorpion_ out on the Hamadian plains, hinting how matters stand. After that communications may have to cease for a while. As for these death-hunters, they will find out presently that they are up against something far more terrible than anything which old Jacob Stendahl or the wood-cutter have ever imagined in their wildest fancy. The secret of the Schwarzwald is not for them. I hold the master-key, Fritz, and when I die that master-key will be broken."

And the two men, who had been aware of the presence of the Englishmen ever since they entered the forest, and had watched them accordingly, now moved off in the same direction which the latter had taken half an hour before.

*CHAPTER XVIII*

*"LIVE WIRES"*

Matters in the Schwarzwald were now rapidly nearing a climax; the final contest between German brains and English wit could not much longer be delayed. For the moment Keane and Sharpe, unknown to themselves, were enmeshed in the network of a deathly trap. Nothing less than a miracle, or something approaching the same, could now set them free from their perilous position. One thing was certain, and that was that this clever but unscrupulous mathematician and engineer, who was now their declared enemy, would not hesitate to adopt the most extreme measures to get rid of his unwelcome visitors. Unfortunately his power, which almost approached the supernatural, made him a dangerous and a wily foe.

It was now past midnight, but the two Englishmen, who had left the track some time before at a point where its course was suddenly changed, and had continued their journey by the aid of a luminous compass, and the uncertain light of the moon, came at last to another halt.

"Let us stay here a while, Sharpe," his companion had whispered. "I have a strong premonition of some impending danger."

"The deuce you have!" remarked Sharpe, who well knew what this meant in a man like Keane, whose psychic faculties were not to be sneered at.

"Yes. I cannot explain it, but there is some hidden danger right ahead of us; of that I am as certain as that we are in the Schwarzwald. We had better lie down a while and await developments quietly."

Nothing loath, Sharpe unfastened his shoulder straps, slid his equipment quietly to the ground, and laid himself down beside his companion.

For the moment all was quiet. The moon was hidden behind a bank of clouds, and it was therefore very dark, but sounds travel far in the night air of the forest, and when they conversed, they spoke only in whispers.

"It may be," remarked Keane, "that the spot we seek is just in front of us, though I cannot see any glade or clearing as yet; it is too dark."

"Is it likely that there are any booby-traps hereabouts, set by this wily professor?" asked his companion.

"I cannot say; he may have some outer system of defence."

"Or even a system of ground signals to announce the approach of strangers, whose presence might be undesirable to him," added Sharpe.

"It is possible," whispered Keane, whose mind was actively engaged in preparation for eventualities, in view of his inexplicable premonitions. Suddenly he started and touched his comrade lightly with his raised forefinger.

"Hist!" he said, in a voice which could not have carried further than a couple of yards Then he carefully raised his head, and, turning his eyes towards the thicket through which they had come, he tried to read the secret which it contained. His alarm was justified, yet was he mystified not a little, for the more immediate danger seemed to come from behind.

"Can you hear it, Sharpe?"

"Yes, the same crackling of twigs; another wild boar," remarked his friend facetiously.

Keane shook his head, for his sensitive ears had told him that the footsteps which he had heard were those of human beings. Nor was he mistaken, for a moment later they both heard distinctly, not merely the crackling of twigs and the rustle of the bracken under heavy footfalls, but voices, human voices, conversing in a guarded and careful manner.

"None of your Schwarzwald peasants this time," he murmured, fingering his Webley already, for he instinctively felt that this time they were beset by danger both before and behind. And indeed, these two men, during all their adventures in the secret service during the war, were never in more deadly peril than at this moment, as they were soon to learn.

Scarcely daring to breathe, much less to whisper now, the two Englishmen watched furtively for the coming of the strangers, who were now less than a score of yards away, but were approaching very stealthily, as though they were searching for something on the ground.

"Who can they be?" wondered Keane. "And what can they be searching for?"

"Poachers," Sharpe was thinking, "merely poachers, searching for their booby-traps."

Nearer and nearer came the dark shadows, and both the airmen had their Webleys trained on them now. In that moment they might have shot them down easily, and before long they would regret they had not done so. But that is not the English way, for the ordinary Englishman would give even a dog his chance, as the saying goes. Still, there are dogs and dogs, and sometimes human dogs are worse than the four-footed ones. But the Englishmen were uncertain; they did not know what world-wide conspirators were these two men. They did not know what fearful deeds would happen even that day on the Hamadian desert, two thousand miles away, but all of it engineered from this spot, and made possible by these two men. And as they did not know, they did not fire, but waited.

"Gott in Himmel, where does that _verdammt_ live wire begin?" asked one of the men in a low but vehement voice. It was the professor himself, searching for one of his own man-traps.

Sharpe glanced at Keane, but the other motioned him not to fire.

"We’re learning something, old man!" he whispered. "This is the gateway to the aerodrome."

The two men had passed them now, passed within six yards, and yet had missed them. They were now groping a little way ahead, looking for secret signs and marks lest they should be hoist upon their own petard.

"Donner und Blitzen! Have you found it yet, Fritz?" called the professor a little louder to his friend.

"Here it is, Professor! Be careful ... there are six wires already laid for those _verdammt_ Englishmen, Keane and--what is the name of the other?"

"Sharpe!" rapped out the professor, as though he had known the man all his life.

At these words the two Englishmen looked at each other in blank amazement. And before their astonishment could subside, the opportunity which had been given to them of ridding the world of two great conspirators had passed.

"One--two--six!" they heard the mechanic say, as he helped the professor over the deadly maze, scarcely fifteen yards in front of them, and then their dark forms had merged into the trees and disappeared, their voices becoming fainter and fainter.

"Great Scott!" gasped Sharpe, when he recovered from his astonishment; "we’ve walked right into the hornets’ nest."

"We should have done if we’d gone another fifteen yards," replied Keane, wiping the perspiration from his forehead.

"Fortunate you had that presentiment of impending danger," said his friend.

"We should have been lying dead and half grilled over his deadly wires but for that strange, weird feeling of mine," replied Keane.

"But there, after all our attempts at concealment, he knows all about us."

"Even our names seem familiar to him," remarked the senior airman, greatly puzzled.

"I cannot understand it," replied the other. "Who can have given him this information?"

"Who indeed?" asked Keane. "It is as great a mystery as the other matter."

"Can it be the woodcutter or the clockmaker, do you think, for Hans is sure to have called at Jacob Stendahl’s cottage and told him the news."

But Keane shook his head, as he remarked: "Neither Hans nor yet the woodcutter could possibly have told the professor our names. This evil genius must have other sources of information at his command. Possibly he has an agent at Mulhausen aerodrome, or even at Scotland Yard. To a man like this, a thousand ways are open. I cannot say, but this I know, we are on the edge of the biggest mystery I have ever encountered."

"And we might easily have shot him. Bah! it would have been better to have fired, Keane," added Sharpe somewhat bitterly. "Cannot we follow him now?"

"No!" replied his companion, firmly. "It is better as it is."

"Why?" demanded the other.

"Rest content, Sharpe," said Keane. "To-day we have discovered the aerodrome; to-morrow we will capture it."

*CHAPTER XIX*

*THE DEVIL’S WORKSHOP*

Patiently, now, the two Englishmen waited for the dawn. Till then it would not be safe to move in any direction. As they lay in the long bracken and ferns, however, they were able to converse quietly, and to discuss their plans for the coming day. The spot they had come so far to seek was now before them. The live wires, just a few feet ahead of them, had been duly located, and now that the danger was known, it was not insuperable. It was an added mystery to them, nevertheless, how this wizard secured sufficient voltage to make these wires so deadly. They assumed, however, that powerful dynamos, worked by this same silent energy that propelled the aeroplane, were at work somewhere near this spot.

Dawn came at last; a faint yellow streak lit up the horizon away to the east. Then a crimson flush revealed the distant tree-tops, and the moon and stars faded away. A hundred songsters awoke the stillness of the forest, for another day had dawned, and the sable curtain of night rolled westward.

"See, there is a clearing fifty yards ahead," were Keane’s first words to his companion.

"It is the aerodrome, the secret aerodrome!" replied Sharpe, peering through the trees.

"Let us work round a little way and find the workshop or hangar. I fancy we shall find it on the other side of the glade."

"Mind those beastly wires, then!" replied Sharpe, as he began to crawl through the dense undergrowth after his companion, who had already started to make a circuit of the outer defences on his hands and knees.

The next half-hour was spent in cautious creeping and crawling just outside those death-dealing wires. At the end of that time, however, Keane made a discovery. He had completed about half the circuit, when, peering carefully through the trees, he fancied he could make out the camouflaged fabric which covered some temporary building. So carefully was this place hidden amongst the trees that he had to look twice or three times before he could make up his mind that he was not mistaken. At last he convinced himself that he had located the workshop, else, why should the place have been so carefully hidden. Waiting for his companion to reach him, he pointed to the object and whispered, "There it is, not thirty yards away!"

"Shall we get over these wires, and rush the place?" asked Sharpe.

"No. Let us continue our journey until we have completed the circuit. We may make another discovery yet. Come along; fortune favours the brave."

They had scarcely crept another hundred yards, however, when a rustling in the leaves, accompanied by a snort, revealed the presence of another wild boar, which had evidently scented their presence.

"Confound the pig!" muttered Sharpe, who was afraid the sounds might lead to their premature discovery. But Keane thought otherwise, for, to his quick mind and instructive genius, this trifling event seemed providential.

"The pig!" he whispered, pointing to the spot whence came the occasional snorts of the angry, disturbed creature.

"What of it?" queried Sharpe.

"Let’s get to the other side of the beast and drive it against the wires."

"And roast the brute alive for the benefit of their breakfast, I suppose."

Keane laughed silently, and wondered how far the conspirators used this live wire to keep themselves supplied with food. He knew, however, that a wild boar on the live wires would soon bring out the inmates of that mysterious house in the woods, and would sufficiently distract their attention to give the airmen their opportunity.

The next moment, having made a sufficiently extensive circuit, so as to get the wild boar between them and the wires, they began closing in on the beast, an operation not devoid of peril, should the boar decide to attack them. Fortune favoured them, however. The angry beast, noting the approach of some unseen enemy, by the movements of the tangled undergrowth, half frightened and half infuriated, made off in the direction of the clearing, uttering further snorts. The next moment he had touched the first of those deadly wires, and, with a wild scream which rang through the forest, he leapt into the air, then fell back quivering but dead across that fatal grill.

"Back--back for your life!" hissed Keane, as he made haste back to the spot where they had sheltered, close to the camouflaged hangar.

The next instant the watchers saw the professor and his assistant rush out of the little building, towards the place where the animal lay right across the first four wires. In their excitement they both seemed to have forgotten the presence of the two Englishmen in the woods during the previous evening, for they were both unarmed. Or perhaps it was that they imagined them to be the present victims of their cunning.

"Hoch! Another royal boar for the larder, Fritz!" exclaimed the professor. "We shall have the winter’s supply complete very soon."

"Gut, mein herr!" came the answer.

"Better go back and switch off the current, so that we can take it away," urged the chief, and, staying but a second to see the royal victim, the assistant complied.

This was what the two Englishmen had been waiting for. The moment of action had come at last. Gripping their pistols, they made ready to advance and take possession of the hangar during the absence of the inmates.

"Sind Sie fertig, Friedrich?" called the professor.

"Ja, das bin ich!" replied the other, as he left the workshop, and rejoined his companion.

"Come along, the wires are dead now," whispered Keane, and, keeping well within the shadows of the trees, the two men crept forward, gained the rear of the structure, then cautiously worked their way round and entered the hangar unobserved.

One glance about the well-fitted workshop sufficed. There were no further occupants, and they lowered their pistols. Sharpe at once sprang to the lever which regulated the powerful electrical current and clutched it. In another instant the two men without would have paid the extreme penalty, for they would have been instantly killed by their own evil device, but Keane stopped him:--

"Don’t!" he said. "We have much to learn. The professor at least must be taken alive, if possible. The secret he holds is too precious to be lost. Let us hide!"

"Where can we hide?" asked the other, somewhat disappointed, and amazed at the further risks which his companion appeared willing to take in order to gratify an insatiable curiosity. "The tables may be quickly turned upon us."

"We can shoot them as a last resort, if that is necessary," urged Keane, who knew the priceless value of the secrets which this place contained.

"Hist! They are coming."

"This way!" whispered Keane, and he drew his companion into a little recess, which had evidently been curtained off for the mechanic’s sleeping berth.

They had barely withdrawn themselves into this narrow apartment when the two men entered, dragging the carcase of the wild boar with them.

"Leave it there for a moment, Strauss. The message from the Rittmeister is due. I must also send him that other message again, as the first has not been acknowledged," were the professor’s first words.

"Yes, sir. Shall I start the dynamos again?" asked the assistant.

"Perhaps you’d better, but first hand me that message book and the secret code."

The next moment the professor was busy at the wireless keys, transmitting some message to the far deserts of Arabia.

"By all the saints," gasped Keane, "he’s sending a message to the raider, the _Scorpion_, as he calls it. I must have that secret code at all hazards. I wonder what he is saying?"

For some time the chief conspirator was engaged coding and decoding messages at the little table where the aerials, carefully hidden amongst the trees without, had their terminus. And in that moment Keane thanked his stars that he had waited for this, for he saw new possibilities opening out before him. Once in possession of this mechanism and the necessary codes, he could communicate at will with the distant raider, who was threatening the whole civilised world by his almost superhuman powers of brigandage. He could recall the raider also, and make his capture certain, once he could secure absolute possession of this little citadel.

For the present he could do nothing but wait, however, and see how matters developed. Once, the assistant came quite close to their hiding-place, and both men again gripped their Webleys. At this moment even to breathe seemed fraught with danger. If the man should enter the little apartment, he must die, and the professor must be immediately threatened with the same penalty unless he surrendered.

"Ha! So far so good!" gasped Keane, as the mechanic recrossed the workshop without actually entering their hiding-place.

"Teufel!" spluttered the professor. "Here is that fool Tempest trying to communicate with those two _verdammt_ Englishmen who are still roaming about in the Schwarzwald. He little knows that we possess his secret code."

"Himmel! What does he say?" asked the other.

"Wants them to report progress at once, and let him know how matters stand," said Weissmann in a mocking tone. "He says he will come over himself, if necessary."

"Donnerwetter! Ask him to come, Professor. He might as well grill with his accomplices on the live wires, for that’s where they’ll be before the day is out, unless they abandon their futile search," replied Strauss.

"This fiend is a perfect wizard!" thought Keane, and his glance signified as much to Sharpe. "How he manages to get hold of these secrets is beyond me. And yet, there is a defect in his mad science, for he does not know that we’re here, and that his own life is in our hands. Fool that he is, he will soon learn that the wit of an Englishman is more than a match for his boasted knowledge," and here the senior airman carefully withdrew a cartridge from his Webley and inserted another, silently--a cartridge that had a specific mission. His companion watched him and repeated the action with his own weapon, for he understood.

"Blitz! but I’ve half a mind to send for Tempest," mused the professor, who was still toying with the keys of the wireless instrument.

"Send for him, Professor," urged his accomplice. "Those Englishmen are getting too close to be pleasant. The British army of occupation will be carrying out a thorough search of the Schwarzwald if these men get away, and then where shall we be?"

"We are in the neutral zone, though," replied the other.

"But we’re contravening the Peace Regulations, sir, and the English will not stand upon ceremony. It will be too late should these men get away."

"Donner und Teufel!" rasped out the angry professor. "Don’t speak to me of the Peace Regulations. There will be no peace till Germany regains all and more than all she has lost. I will send for this Commissioner of Aerial Police, for I believe that he and his two accomplices, Keane and Sharpe, are the only ones so far who know anything that matters about the secret of the Schwarzwald," and he began to tap the keys, reeling out the words as he sent them.

Keane listened acutely for the cyphers of the code. They were:--

"Z--X--B--T--V--O--P..."

and he understood that Tempest was to come at once, make for Mulhausen aerodrome, then take a bee-line, east-north-east over the Schwarzwald until he saw a smoke column, where a suitable landing-ground would be found, and his accomplices would await him.

"Ach!" shrieked the professor, with a fiendish laugh. "The smoke column will mark his last resting-place. They shall all be buried together, these mad Englishmen. We will have more live wires stretched across his landing-ground, and as the wild boar died, so will these men die who dared to follow me into the Schwarzwald."

"The wild boar! Hoch! Hoch!" exclaimed his companion. "It is a fitting tribute for the English are swine!"

"And the _Scorpion_ shall witness the inglorious end of these men," cried the professor, as a sudden idea came into his mind.

"Der _Scorpion_?" queried Fritz, looking up amazed from his task. "What do you mean, Professor?"

"Why, the Rittmeister will have finished his work in the Hamadian Desert this afternoon. His instructions are to resign the Sultanate of those regions for the present, for the skies will be thick with British scouts by to-morrow."

"But then he goes to Ireland to work with the revolutionists there, does he not, mein herr?"

"Ja! ja! but I will ask him to call here for a day or two before he proceeds. He will have much to tell us, and Spitzer, Carl and Max would like to see these dangerous opponents safely out of the way, for at present they are the only enemies to be considered."

"Gut!" ejaculated Strauss, catching something of the professor’s enthusiasm.

Keane would have intervened before this, for he had noted Sharpe’s impatience, but he intimated as well as he could by mute signs and otherwise, that the fiend was doing their work for them.

"Let him send this message first," he whispered in his companion’s ears, "and then----" But the sentence was completed by further cabalistic signs.

Again the professor turned to the keys, and sent his last instructions through the ether waves to his confederate, the brigand of the eastern skies.

*CHAPTER XX*

*"HANDS UP!"*

"Haende in die hohe!" cried Keane as soon as the last message had been sent.

"Der Teufel!" gasped the professor as two swift shadows darted out from behind the curtain, and the two men whom he had just been discussing with such utter contempt confronted him and his accomplice with gleaming pistols.

"Hands up!" repeated Keane, anxious to give the professor another chance.

With a blasphemous oath the man of evil genius, who saw that he had been outwitted, reached for a small hand grenade which lay beside him on the table, and shouted:--

"Never!"

"Then take that!" cried the Englishman, and two puffs of greenish smoke, following a sharp crackle, burst simultaneously from the pistols, for they had both fired together.

The new Asphixor bullets took immediate effect. Both the Germans staggered, clutched their throats as though to ward off the effects of this new powerful gas recently discovered and adapted by that eminent British scientist, Sir Joseph Verne--then lurched and fell, whilst their opponents stepped back and quickly fitted on their safety masks.

"They are both sound asleep," observed Keane, when, the fumes having cleared away, he threw aside his respirator and carefully examined the unconscious men.

"Let them sleep," said Sharpe, who would have adopted even more drastic measures if he could have had his own way. "’Tis scant mercy they would have shown to us if we had been in their power."

"And now let us get to work, for they will awaken in seven or eight hours, and we have much to do. We must prepare for Colonel Tempest, and also for this raider," urged Keane.

"But they will not come to-day, Captain."

"Scarcely, but we must be prepared for anything. There are only a couple of us."

"Shall we secure these men, in case they awake earlier than the stipulated time?"

"No, let us remove their slumbering forms behind the curtain there; we will attend to them before they awake. I do not like the idea of strapping down unconscious men, even though they are criminals. We will watch them from time to time."

Then for the next half-hour they carried out a careful examination of the hangar and its contents. They were amazed at the intricate and wonderful mechanism with which the place was fitted. It seemed impossible that these things could have been transported hither without attracting attention. Parts of aeroplane wings, struts, propellers, engine-fittings, strange, weird-looking cylinders, retorts, analytical appliances, instruments and vessels for chemical research, powerful but silent dynamos, and numberless other things, all neatly arranged, and apparently in working order, half filled the place.

The further they carried their investigation the more were these two Englishmen bewildered by what they saw.

"Is it possible," gasped Keane, "or am I only dreaming? We have discovered the home of the super-alchemist. After this, nothing will surprise me."

"We have discovered the devil’s workshop," replied Sharpe, who did not appear to be half so enraptured as his friend.

"Nay, we shall find the philosopher’s stone, or the _elixir vitae_ soon," replied Keane, continuing his investigation.

"We are more likely to find the _elixir mortis_ than anything else," said the gloomy one. "This place gives me the shivers. I am sure that I shall have cold feet for the rest of my life."

"After this, Hermes and Geber will be dull reading," continued the enthusiast. "Give me the Schwarzwald every time for the real thrill of the alchemist."

"Their time might have been more profitably employed, at any rate," remarked Sharpe.

"Yes, it is a thousand pities that the wonderful brain which designed and organised all this should have had nothing better in view than brigandage and world revolution."

"More misdirected energy," moaned Sharpe; "the greatest brains often make the greatest criminals."

"You’re a veritable misanthrope, Sharpe!" said his companion, laughing.

"I have reason to be," returned the other.

"What do you mean?"

"I mean this--we’re not out of the wood yet."

"I agree; we’re in the very centre of it," replied Keane.

"Yet you did not inflict the _coup de grâce_ on the diabolical vipers, and they will shortly awake. Moreover, the _Scorpion_ may arrive unexpectedly, and we shall be unprepared for her."

"What would you do?"

"Bring over the machines from Mulhausen, ready to fight this air fiend when he comes."

"Ho! So you’re longing for another real air fight, are you, like the ’scraps’ we used to have with the Richthofen ’circus’?"

"At any rate, we’d better prepare. Then I’d bind those two criminals hand and foot or surround them with live wires, so that, should they awake unexpectedly, they would not dare to stir."

"There is certainly something in what you suggest about bringing the aeroplanes over, though we should have a deuce of a job to land them in this place; they’re by no means possessed of the powers of a helicopter. However, I’ll get into touch with Colonel Tempest and ask for immediate assistance, and also ask him to bring over Professor Verne to investigate these mysterious engineering and chemical appliances."

So, leaving the workshop, the live wires and the prisoners to the care of Sharpe, the senior airman devoted all the rest of that morning to investigating the wireless apparatus, examining the secret codes, and trying to get into touch with the Commissioner of Aerial Police. In this, however, he was not very successful, for the air was full of messages, concerning an overdue air-liner which had been expected for some time at Cairo. Perhaps his message had been jammed or lost in the aerial jostle.

Colonel Tempest was almost at his wits’ end. He sorely needed the help of his able assistants. He wanted to send them out east to chase this daring brigand off the trade routes.

He was unable also to comply with the request for assistance, when at length it did reach him, for all his best fighting men, with the exception of these two in the Black Forest, had been sent after the raider. He promised, however, to come personally at the earliest possible moment, as soon as matters had been cleared up a little.

Again and again Keane tried to reach him with brief, but urgent coded messages, for he was now getting extremely anxious lest the raider should appear before they were ready. Sharpe, however, who was eminently practical, had taken the professor’s own tip, and had laid wires across the glade, which, when properly connected up, would make it a dangerous proceeding for a hostile aeroplane to land there, while, in the event of a friendly one appearing, the current could be immediately switched off. He had seen to the prisoners as well, for, unknown to Keane, he had, on the first signs of awakening, given to each of them a sufficiently strong soporific to extend the period of their quiescence for a considerably longer period, so that, late that afternoon, his friend was somewhat alarmed at their quietude.

That night they watched in turns, and relieved each other every two hours. When morning came they climbed the highest trees and scanned the horizon in every direction for the promised help, and also for the _Scorpion_. But although the column of smoke from the fire which had been lighted, ascended all day in one long grey streak to guide the British airmen, yet morning wore on to afternoon, and no assistance came.

Keane sent message after message, but apparently to no purpose. The very heavens were full of messages, for the whole civilized world had been roused by the last daring feat of the phantom airman. London, Paris, Cairo, Delhi and New York were clamouring for his immediate capture and execution. Strong things, too, were being said about the incapacity of the much vaunted aerial police, but all the world realised that the task before these men was almost superhuman.

Twice an urgent message came recalling the two Englishmen, but Keane replied with the one word, "Impossible!"

And all this time the raider, who was carefully hiding for a few days, delighted his companions by retailing with much gusto such of these messages as he had been able to piece together from the aerial jumble.

"Let them send all their available machines and pilots out east," he had said to Carl and Max, "then we will quietly slip across Europe to Ireland, where everything is ripe for the promised revolution."

"And the Schwarzwald?" queried Max.

"Oh, we will call there for a few hours en route," replied the pirate, calmly relighting his pipe, "The professor will understand our silence and inactivity."

So the third morning came, and Keane, whose anxiety regarding the still sleeping prisoners had been allayed by Sharpe, who smilingly confessed what he had done, now became fearfully uneasy as to the condition of affairs.

"For heaven’s sake light that beacon again!" he ordered. "If assistance does not arrive to-day, all these secrets I have endeavoured to rescue will be lost."

"What will you do?" asked his companion, who was already applying a match to the pile of dried tinder and sticks.

"Blow the whole place up," he replied.

"And shoot the prisoners?" ventured his friend, slyly.

"No."

"What then?"

"Rouse them up, somehow, handcuff them together and take them away."

"Some job that," remarked Sharpe, looking up at the long thin trail of smoke, for there was still an absence of wind currents.

Even as he gazed into the sky, however, he caught sight of a tiny speck hovering at twelve thousand feet, and he almost shouted, "Aeroplane!"

"Where?" asked his startled comrade, whose nerves had undergone some strain during the past few days.

"Right up in the blue. There, can you see her?"

"Yes, I have her now, but she’s very high. Can it be the _Scorpion_, do you think?" asked the senior.

"Cannot say yet. I’ll fetch the glasses."

"Run for them, quickly! I cannot hear her engines at all. It must be the brigand."

"Ah, there, I hear the engines now, very faintly, though. Rolls-Royce engines too, thank God!" exclaimed Keane fervently, as he recognised the well-known sound, and knew that assistance had arrived at last, in the shape of at least one Bristol Fighter.

"It’s all right, Sharpe. Cut off that beastly current. Tempest will be here in a minute."

"Are you sure it’s Tempest?"

"Yes. Listen to that! Now he’s cut his engine out again, and he’s coming down. It’s the chief right enough; I should know his flying amongst a score of aeroplanes."

The wires were cut off, a temporary landing-tee quickly rigged up on the ground, and frantic signals were made to the pilot, who was now rapidly coming down in sharp spirals.

A few minutes later the intrepid pilot flattened out above the tree tops, dipped again, banked steeply, and sideslipped almost to the ground, in order to get into the confined and narrow space which served the _Scorpion_ for an aerodrome. Scarcely had he landed when another machine, which had followed him from England, performed the same highly-skilled manoeuvre, and taxied up to the little group.

*CHAPTER XXI*

*THE COMING FIGHT*

"Good-morning, Colonel!" cried the two airmen, saluting their chief smartly, as he still sat in the aeroplane, looking not a little crabbed and sour, as he secretly swore at the infamous stretch of ground misnamed an aerodrome; then turned his gaze upon the two airmen who had appealed for assistance.

"Morning! So this is where you young cubs spend your holidays, while the whole world is ramping at me for not catching this infernal brigand. What have you got to say for yourselves?"

Keane was not at all put out by this dour greeting; he knew his chief too well, and admired him accordingly. Merit is not always accompanied by a bland and urbane countenance, neither do brains always accompany a white shirt front.

"I have that to say which will almost make you jump out of your skin, sir," replied Keane, "but we must somehow get these aeroplanes under cover, or properly camouflaged, for the _Scorpion_ may arrive any minute."

"Eh? What’s that you say, boy?" exclaimed Tempest, leaping from the fuselage. "The _Scorpion_?"

"Yes, sir."

"Why, that is the name of your infernal raider, isn’t it, Captain Watson?" and here the colonel turned and addressed his passenger, who was none other than the skipper of the air-liner which had been so roughly handled in the Hamadian Desert.

"The same, sir."

"And the professor, Keane? I sent you to track the professor. Have you found him?"

"He is our prisoner, Colonel," and Keane bowed stiffly, and pointed to the half-hidden hangar, where the two prisoners, who were now partly roused, had been safely secured.

An exclamation of pleasure and surprise broke from this dour-looking man when he heard this news, and his face became wreathed with smiles as he advanced to both Keane and Sharpe, shook them warmly by the hand, and said:--

"Thank you, my boys; I knew if it could be done you would do it, though I could ill spare you for the job. Yesterday my reputation was in shreds; I am to be charged with inefficiency, and a public enquiry is to be held. But you two wolf cubs have re-established my character; I can never thank you enough. Now lead on, show us this evil-minded genius! Professor Verne here, who has come in the second Bristol, with Captain Hooper, is anxious to see him. He may redeem him yet from the error of his ways, and it is vital that this secret of his should be in other and better hands, else it will always be a danger to the public."

So, whilst the party were conducted indoors, and shown the marvels of the modern house of alchemy, the two professors were introduced, and began a series of disputations, very embittered at first, as the German, though relieved of his bonds, and made as comfortable as the circumstances would permit, resolutely refused to give any particulars of his discovery, or even to display the slightest amiability towards his distinguished visitor, though they were not unknown to each other, and had even studied at Heidelberg together in their younger days.

Meanwhile, all possible steps were taken to prepare for the possible arrival of the _Scorpion_. The Bristol machines, after being carefully stowed away in a gap between the trees, were so camouflaged by branches of pine and larch that they presented but a very indistinct object from the air, and, unless their presence were known, might easily remain unobserved.

After some time had been spent in examining the highly developed and intricate mechanism of the devil’s workshop, as the place was now called, the Commissioner suddenly turned upon his chief mentor, and said:--

"By the way, Keane, have you discovered any drawings or designs of this wonderful aeroplane? I don’t see any amongst this pile of papers, and the professor does not seem inclined to help us at all."

"No, sir. We have searched the place carefully, but we have found nothing. Part of the machine could certainly be reconstructed from those spares, but all the important parts are missing. I have an overwhelming curiosity to see the machine, though, and hope that I may not have this pleasure much longer delayed."

"Then we have nothing but these photographs," returned the captain.

"Photographs?" echoed Keane.

"Yes. Why, I forgot to tell you in the bewilderment and excitement of the last hour, that Captain Watson here managed to secure three snapshots of the raider in mid-air, whilst his airship was being attacked."

"It was the boy Gadget who secured them, sir," interposed the air-skipper, anxious to give credit where credit was due.

"Oh, yes, Keane, I ought to say that it was a smart little beggar called Gadget, a stowaway, who really secured the photographs, and hid them away from the brigand. We must see that the little chap is properly rewarded when we return."

"Let me see the pictures, sir," requested Keane, eager to get some idea of his future opponent.

"Here they are. I have had them developed and enlarged. They should be extremely useful to us, as we shall shortly have to encounter this Sultan Selim, Air King of the Hamadian Desert, the world’s greatest bandit, who had the audacity to send me this document by the captain."

And here the colonel, having retailed the whole story of the fight in the desert, showed the brigand’s letter, which had been brought to London the previous day by the fast aeroplane which had carried the skipper of the air-liner.

Keane turned in amazement from the clear photographs of the phantom-bird to the brief, audacious letter of the phantom airman, and read as follows:--

"To Colonel Tempest, D.S.O., M.C.,

Commissioner of Aerial Police, Scotland Yard, London, W.C.

"Greetings from Sultan Selim, Air King of the Hamadian Desert. I regret to inform you that of late there has been a serious increase of aerial crime in these regions. The frequent passing of large airships containing mails and other commodities, without due payment of tribute to my customs officials, is a serious infringement of the laws of my dominion. This action not only imperils the liberties of small communities, but is also a crafty form of aerial brigandage, inasmuch as it defrauds my exchequer of its just and equitable revenue. This practice must cease forthwith, and I have taken steps to-day which, in my opinion, will render it unwise for this shameful trespass to continue. The bearer of this letter will give you further details of the action which I have been compelled to take on behalf of my subjects. Your five missing scouts will be found between the wells of Nefud and the Hedjaz coast. I have destroyed their machines as a salutary warning to future violaters of these my dominions."

Keane could scarcely restrain a smile when he laid down this wily, half-humorous, half-threatening epistolary from the aerial pirate.

"What do you think of it?" asked the colonel.

"It’s a topping letter, sir, but I think he’s trying hard to be funny, this von Spitzer, as you call him. A German with a sense of humour, sir, that’s the best way to regard him," replied the airman.

"Humour indeed!" rasped out the colonel, becoming ruffled. "It’s confounded impudence, and worse, when you remember that, apart from the damage to the airship, which is considerable, there is a net loss of specie and other valuables--to wit, the Maharajah’s jewels--which is estimated at a quarter of a million sterling. I only hope and pray that we may encounter and waylay this bandit before he does any more damage. The deuce only knows what he’ll do next, or where he’ll go."

"Ireland is to be the scene of his next adventure, sir," remarked Keane.

"Ireland?"

"Yes, sir."

"Are you sure?"

"I heard the professor say so. They are to work hand in hand with the revolutionists there, and stir up strife which will make that unhappy land a still greater thorn in the side of Great Britain."

"Just what I feared!" exclaimed the now irate commissioner. "That explains partly those mysterious messages and rumours floating about Dingle Bay, and unfortunately I have had to withdraw nearly all the aerial police from that quarter to send them out east."

"You might as well recall them, sir."

"Why?"

"The raider has left the Hamadian Desert by this time, and is in hiding somewhere, but will call here on his way to Ireland."

"H’m! We’re being thoroughly fooled, and if you hadn’t found this demon’s nest I should have gone mad. At any rate I should have been compelled to resign my post."

"Still, public opinion had to be satisfied, and you sent the patrols where the public demanded that they should be sent. Besides, if you recall them now, this raider will probably pick up your messages and change his tactics. I can tell you this, Colonel, that while he can get his necessary supplies of uranis, and a few extra spares from the workshop here, this von Spitzer intends to carry out his mad policy of destroying the civilized world by piecemeal. It is all part of a great plan to save Germany from the evil consequences of the Peace terms. But, whilst we hold this citadel, and retain these two men captive, his activities are limited to his present supply of this secret element--uranis."

The colonel swore under his breath, and went to examine the prisoners, to make sure that there was no chance of their escaping, for he felt the truth of Keane’s words. He now felt grateful that the airman had not responded to the message for his recall, although it had amounted to a serious breach of discipline.

"Ah, well," he said at length, "it only remains to capture this raider, and the whole system of their clever and daring attempt to convulse the Allies, break up their international system of mail transit, stop the intercourse of civilized nations, and cause a world revolution--all these things will fail."

So their efforts were redoubled to make preparations to capture the wonder ’plane, should it descend on the aerodrome. A couple of machine guns were found, and mounted, under the charge of Sharpe and Captain Hooper, though the skipper of the airliner pointed out that the _Scorpion_ carried bullet-proof armour.

"You will need to hit her in a vital spot," he said, "so that your first burst may be your last, or she will be up again like a helicopter."

"Then we must have the two Bristols ready," urged the colonel, "though it’s a deuce of a hole to get out of with this new type of a Bristol Fighter."

"And the petrol, sir?" asked Keane, who, was rather anxious on this point, for he hoped that the _Scorpion_ would become his victim in the coming air fight.

"There may be sufficient for another two hours, certainly not more."

"That means unless the _Scorpion_ chooses to stay and fight, she’ll simply leave us."

"Von Spitzer will fight unless I stop him!" called out the professor from behind the curtains, where he was confined under the charge of his colleague of other days, for he had been listening to the conversation.

"So much the better!" replied Keane, tartly.

"And when the fight is over there won’t be many of you left alive to tell the story," came the rejoinder.

*CHAPTER XXII*

*AN AERIAL DUEL*

"Message from the _Scorpion_, sir!" cried Keane, a little before midday, from the little key-board where he had been patiently waiting for the last hour.

"Good! What does the brigand say?" asked Tempest.

"Expects to be here within an hour."

"Then we haven’t a moment to lose," replied the colonel. "At the same time, I am glad we have had this message, for to be forewarned is to be fore-armed."

Then, turning to Keane, whom he knew to be his best and most brilliant pilot, he said, "Where would you like to be stationed, boy?"

A sudden gleam came into the youth’s eyes, for he saw that his chance had come.

"Let me have all the spare petrol from the other machine, and let me get up above the clouds in that new No. 7 Bristol Fighter which you brought over, sir."

"I’m afraid it means certain death for you, my lad," replied the chief, after a pause, unwilling to permit the youth to take such unknown risks, and yet still more unwilling to deny him his request. "This _Scorpion_, according to Captain Watson, must be some stunting machine."

"I am willing to take the risks, sir," replied Keane. "It is not my first fight with a Hun."

"Don’t I know it, boy!" replied the other, gazing with fond admiration into the frank and pleasing face of the pilot. "The ribbons which you gained speak for themselves, but they don’t tell half the story. Don’t I remember the morning when you went over the line by yourself, and encountered seven enemy machines, how you fought with them for an hour and brought five of them down, chased the others till your machine threatened to break up, then turned and staggered home with your wings shot to ribbons?" and the colonel fondly patted the youth’s shoulder.

"Then let me go, sir. The brigand will be not a little confounded to find himself attacked both from the ground and the air at the same time."

"You shall go!" said the colonel after another pause. "Will you take a gunner with you?"

"No, sir. I would rather go alone."

And while the petrol was drawn off from the other machine, No. 7 was brought out, filled up, and tested, ready to start at a moment’s notice. The Vickers gun, fixed forward to fire through the propeller, was carefully examined, and several drums of the new armour-piercing bullets placed in position. Another moment was given to the alignment of the gun-sight, a matter of supreme importance in an aerial duel like this one promised to be, for the slightest error in this respect would be like courting disaster.

Ten minutes later the signal was given to stand clear, the colonel himself swung the propeller, and, instantly, the powerful 350 H.P. Rolls-Royce burst into life with a crackle and a roar, and, when the chocks were withdrawn, the Bristol dashed across the ground, leapt into the air at sixty yards, and by a steep climb just cleared the tops of the trees on the edge of the forest.

"What are his chances, Colonel?" asked Captain Hooper.

The chief shook his head as though doubtful of the result, then, after watching the machine for a moment, as it climbed in rapid spirals up into the clouds which half covered the sky at four thousand feet, he said:--

"There is no pilot aboard the _Scorpion_, or any other machine for that matter, who can hold a candle to Keane, but--it is the amazing speed and climbing powers of the other machine that I fear. Still, it will be some fight, and if we fail to trap the brigand down here, well, it is just possible, despite his disadvantages, that Keane may bring the rascal down. He’ll have to keep well out of sight, though, and run at less than half-throttle behind that cloud bank till the moment comes to strike. And now to stations, all of you, and keep well out of sight. Professor Verne, I am afraid you will have to take charge of the two prisoners. Don’t let them get away for heaven’s sake. You must shoot them first."

"I’ll take care of them, Colonel," replied the eminent man, "though it is a somewhat unusual occupation for me."

"Needs must when the devil drives, Professor! I told you it would be some desperate adventure. Have you had any luck with that evil genius, yet?"

"Not the slightest, so far. He is prejudiced against the English mind, and is secretly rejoicing over the expected arrival of the _Scorpion_."

"Tell him from me, Professor, that if he attempts to escape, I shall shoot both him and his accomplice without the slightest compunction," said the colonel, as he turned away to re-examine all his defensive posts, and to alter the position of one of the machine guns, which had been entrusted to Captain Sharpe.

Fifteen minutes passed away, and the Bristol, hidden away behind the cloud bank, kept its engine well-throttled down, lest the roar of the powerful motor should reveal its presence, when, suddenly, from one of the watchers, the cry arose:--

"Aeroplane approaching from the south-east."

"Is it the _Scorpion_, Captain Watson?" the colonel asked, as soon as the machine had been located.

"Yes, it is the same brigand, sir."

Then, with amazement bordering on the supernatural, the little garrison saw the _Scorpion_ moving across the sky at a miraculous speed, and making directly for the secret aerodrome. Once or twice it circled around at three thousand feet, then dived a clean two thousand five hundred upon its objective, silently, like a mysterious phantom bird. At five hundred feet it flattened out, rode gaily above the tree tops, then swooping like a falcon, once more touched the ground lightly, and came to rest within thirty yards of the secret hangar.

"Haende in die hohe!" cried Colonel Tempest, stepping out into the open, and confronting the visitors with a couple of revolvers, as they prepared to leap from the armoured conning-tower.

"Ach Himmel! We are betrayed!" cried Spitzer. "The _verdammt_ English have captured the aerodrome."

Without thought of surrender the brigands tumbled swiftly back into the armoured cell, just as a shower of bullets from both revolvers swept the upper surface of the cockpit.

"Fire!" shouted Tempest, stepping back, as the daring bandits, regardless of the danger, started the propellers once more by means of the self-starting knob, within the conning-tower.

And the next instant, even as the machine turned and raced for safety, a terrific hail of bullets from the two machine guns swept the _Scorpion_ from stem to stern. One of her machine guns was swept from its mountings, and it is believed that one at least of her crew was wounded, probably by the Colonel’s revolver shots, but as for surrender, the pirates would have none of it, as, apparently unhurt in any vital spot, the _Scorpion_ recrossed the aerodrome, staggering once or twice under the fierce welter of bullets, managed to leave the ground, and sail over the tree tops out of immediate range.

"Confound it! She’s absolutely bullet-proof!" shouted the colonel, who was furious at his failure, for his object had been to capture the machine and its crew wholesale, because of its valuable secrets.

"We shall see no more of her!" exclaimed Captain Hooper.

"Just wait a moment," said the skipper of the air-liner. "She’ll have something to say presently. You don’t know these infernal brigands."

The last speaker was right, for a moment later the infuriated Spitzer, sweeping round at a frightful speed, swooped down upon the little hangar, where he presumed the English were in possession, swept the place with a burst of machine gun fire from his remaining gun, then dropped a bomb filled with high explosive right into the middle of the structure; whilst he, himself, was screened by the trees from the enemy’s fire.

The roar of the explosion was deafening, and several trees in the vicinity of the workshop were blown to fragments, whilst the workshop was now a tangled mass of wreckage. It was also burning furiously, and a thick pall of dense smoke already hung over the spot.

"The professor!--we must save him!" cried Tempest, who was already limping from a bomb splinter which had pierced his leg.

Captain Watson ran to help him, but the two machine gunners, Sharpe and Hooper, stuck to their posts ready for the next attack, which they knew would not be long delayed, for Spitzer, during his last circuit, had marked the position of the two machine gun posts.

As the rescuers hastened to the assistance of the prisoners, they came upon Professor Verne, bleeding from the hands and face, dragging the prostrate form of the German from amid the burning wreckage.

"Ah, you are wounded?" cried the colonel.

"It is nothing," replied the other. "See to the mechanic. I fear he is killed, poor fellow, by his own countrymen."

It was so; his mangled form was found buried under the _débris_ of the workshop. The German professor and his rescuer were both helped to safety; then the battle began again.

"Here comes the _Scorpion_!" shouted Captain Watson. "Look out there!" and instantly the air resounded with the sharp, short crackle of the air brigand’s gun--

"Rep-r-r-r-r-r----!" as the raider swept the machine gun posts.

At this very instant, however, the sound of whistling wires came suddenly from overhead, as something swooped down from the dizzy heights upon the attacker. Then the sharp crackle of a Vickers gun rent the air, as, in a headlong dive of two thousand feet, the Bristol Fighter hurtled down, spitting fire through the whirling propeller, and driving its quarry almost to the ground by its unexpected onslaught.

By a miracle almost, the _Scorpion_ escaped a terrible crash, flattening out within two feet of the ground in the middle of the glade, then started its upward climb to out-manoeuvre its new opponent, for the rest of this terrific combat was confined to the air.

The little garrison below came out to see this thrilling spectacle, and even the wounded German raised himself to watch the _Scorpion_, as he expected, give its _coup de grâce_ to its clumsy opponent. The fight now was for altitude, dead angles, and the blind side of each opponent, but more especially for altitude, for this is the equivalent in an aerial duel of the windward position, in the days of the old frigates.

Once, after climbing on the turn, the two machines approached each other dead on, and each opened a burst of fire simultaneously on its opponent. Carl, the scout pilot, was handling the solitary gun, and, if his aim had been more steady, that would have marked the finish of the fight. On the other hand Keane’s bullets pattered with unerring aim upon the armoured conning-tower, but with little effect, for so far the finely-tempered steel resisted even these armour-piercing bullets.

The watchers down below trembled with rage--all save the German--when they saw this fearful waste of markmanship, but up there, calm and collected, the British pilot clenched his teeth and muttered:--

"I must find his dead angle! I will attack him from below."

Then followed a series of thrilling manoeuvres, in which the daring skill of the Englishman alone saved him from his too-powerful opponent. The _Scorpion_, using its superior speed, made a desperate effort to sit upon its opponent’s tail, a deadly position if it could only be attained. But, looping, banking, sideslipping and occasionally spinning, the Bristol out-manoeuvred its enemy every time.

"Shade of Richthofen!" exclaimed the infuriated Spitzer; "but this _verdammt_ Britisher is some pilot."

Carl had become nervous and agitated at the gun, and his shooting had begun to annoy his leader, who shouted angrily, "Let Max take the gun, dachshund!"

But Max was huddled up in the bottom of the cockpit with an English bullet through his head; he had fired his last shot.

"Blitz! Here he comes again!" shouted the German pilot, as his opponent in the roaring Bristol, with engine full out, made as though he would ram his enemy in mid-air, though such was not his intention.

"Himmel, what does he mean?" yelled Spitzer, as he also opened out to avert the threatened collision, then pulled over the controls, stalled his machine, and attempted a vertical climb.

"Thanks be!" muttered Keane, for this gave him just the opportunity he sought. For two brief seconds the nether part of the fuselage, the only weak spot in the _Scorpion_, was exposed, and with a quick eye and unerring aim the British pilot poured a short burst into the very vitals of his enemy, then dived for safety.

It was the end of the fight, for the armour-piercing bullets ripped through the softer, thinner steel of its victim, passed through the chamber where the high-pressure cylinders which contained the uranis were kept, and weakened or cracked one of those deadly things, which were at once both the strength and the weakness of the _Scorpion_--the only thing, as her pilot once said, that its crew need fear.

Down, down sped the Bristol, as though conscious of the terrible catastrophe which would shortly follow. It was well that she did, for, ten seconds later, it seemed as if the end of the world had suddenly come.

Even while the _Scorpion_ was poised in mid-air, in the very act of her last vertical climb, with nose pointed to the skies, the frightful explosion occurred. The terrified onlookers threw themselves flat upon the ground, but even the earth rocked, and huge trees of the forest were uprooted. It was as though the mighty concussion had veritably blown a hole hi the universe. The _Scorpion_, with all her crew, disappeared as if by magic, blown into ten thousand fragments, and scattered like blazing meteors to the very extremities of the Schwarzwald, while the British aeroplane did not escape but crashed to earth, with its unconscious pilot still firmly holding the controls.

Thus did the _Scorpion_ meet her end, after all the vaunted pride and skill of her founders. In that place where she was born, there also did she come to an inglorious end, in the very presence of the evil-minded genius who had designed her. Even the dying German professor at last saw the error of his ways, and wished, in his latest hours, that his energy and skill had been devoted to a purpose more lofty and humane.

The great shock of that mighty explosion was felt for a hundred miles and more. In far distant lands the seismographic instruments recorded its effects. Some said that a great earthquake had occurred in central Europe, but the Allied Command on the Rhine thought that some mighty secret ammunition dump in the Schwarzwald had been accidentally destroyed, and they sent assistance in every shape and form. And the first to arrive were the aerial patrols, with medicines and supplies, for the survivors on that blackened, devastated aerodrome.

The unconscious pilot was extricated from the wreckage of the Bristol Fighter, and after months of careful nursing he was restored to convalescence, but he will never fly again. For his daring deed, he was honoured by his country, and decorated by his King. Sharpe, Hooper and Captain Watson, though severely wounded, recovered from their injuries. Professor Verne had a miraculous escape from death when the brigands bombed the hangar, and Colonel Tempest--though for the rest of his days he will limp with the aid of a stick--was mighty glad to lay down his high office with a reputation untarnished, and with the added honour of a knighthood, and a substantial pension.

It now but remains to tell what happened to that brilliant but misguided German, the renowned Professor Rudolf Weissmann. He lingered for another day after the terrible event which had befallen his fortune, and his friend Sir Joseph Verne, constant as ever, waited beside him and tended him amid his sufferings, for there is a wonderful spirit of brotherhood and fraternity amongst men of learning. They are the children of no particular country, for their parish is the world, and, like our own Shakespeare, the whole earth claims them for its own.

And when he saw that the time of his departure was at hand, this erring genius no longer tried to withhold from the world the great secret which he held, but, desiring to make what amends he could for the evil he had wrought, he freely offered to reveal the secret to his old time friend and fellow-student.

But, alas, he had left it too long. The candle of life was flickering within him, and the end was too near. Even while, with true repentance, he endeavoured to give the hidden formula of the mysterious uranis to his friend, he fell back exhausted and his spirit fled.

So the wonderful secret was never revealed, for it lies buried deep in a thousand fragments, amid the dark recesses of the Schwarzwald. But Hans, the clock maker, and his friend Jacob Stendahl the wood cutter, and many more beside, who dwell amid the legend and folklore of the Black Forest, still assert that at certain times, especially when the full round moon casts its silvery light over the Schwarzwald, the peasant who treads these lonely paths may see the phantom airman on his ghostly ’plane.

* * * * *

As for Gadget, the little urchin of a stowaway, the sharp-witted, up-to-date cabin boy who photographed the raider in mid-air, and rendered such valuable service to the authorities, he was duly rewarded. The Commissioner of Aerial Police pinned a gold medal on to his little tunic, soon after the great air-liner returned to London, and even delivered a speech in his honour, congratulating him upon his resourcefulness and courage.

He is no longer a street arab, for Captain Watson has adopted him, and sent him to a preparatory school, where he is pursuing a useful course of studies. But, when the long summer holidays arrive, you will find Gadget, dressed in a smart little uniform, with plenty of gold braid about his cap and tunic, standing beside the captain or the chief officer, in the navigating gondola of the _Empress of India_. All who know him speak highly of him. And there are even those who believe that this little, mischievous, up-to-date cabin boy and erstwhile stowaway will one day be one of out great air-skippers.

THE END.

THE LONDON AND NORWICH PRESS, LIMITED, LONDON AND NORWICH, ENGLAND

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*THE GREAT ADVENTURE SERIES*

_Titles uniform with this Series_

*Percy F. Westerman:*

The Airship "Golden Hind" To the Fore with the Tanks The Secret Battleplane Wllmshurst of the Frontier Force

*Rowland Walker:*

The Phantom Airman Dastral of the Flying Corps Deville McKeene: The Exploits of the Mystery Airman Blake of the Merchant Service Buckle of Submarine V2 Oscar Danby, V.C.

S. W. PARTRIDGE & CO. 4, 5 & 6, SOHO LONDON, W.1.