Sign of the Green Arrow A Mystery Story by Snell, Roy J. (Roy Judson)

Online Distributed Proofreading Team (http://www.pgdp.net)

Transcriber's note:

Text enclosed by underscores is in italics (_italics_).

A Mystery Story

SIGN OF THE GREEN ARROW

by

ROY J. SNELL

Reilly & Lee Chicago

Copyright 1939 By Reilly & Lee Printed in the U.S.A.

CONTENTS

CHAPTER PAGE I "This is Our Secret" 11 II Spooky Waters 22 III A Bright Eyed Beach-Comber 34 IV Spies 46 V Whispering Depths 54 VI Real Progress! 73 VII Mystery Singers of the Night 82 VIII Monster of the Deep 96 IX Dave's Electric Gun 105 X Little Big-Heads 115 XI Tigers of the Sea 125 XII Johnny's Day Off 136 XIII The Green Arrow Trail 150 XIV An Important Discovery 161 XV Adrift in the Depths 167 XVI Voice of Drums 174 XVII Marching on the Castle 183 XVIII The Battle 192 XIX On the Bottom 204

SIGN OF THE GREEN ARROW

CHAPTER I "THIS IS OUR SECRET."

It was midnight. Johnny Thompson paced the deck of the _Sea Nymph_ alone. He would be doing this until daybreak. The tropical night was glorious. There was a faint breeze--just enough to ripple the waters where the phosphorescent light thrown off by a million tiny creatures rivaled the stars above.

"Spooky," he thought, meditatively. "Out here all alone with the night.... Natives over there." He faced the east, where dark green hills loomed out of the water. Over there was a small island. Johnny never had been there. Some time he'd get into a canoe and paddle over. Earlier in the evening he had seen a light, a white man's light, he had thought, without knowing why. He--

His thoughts were interrupted by someone moving, up forward. Or was there? He had supposed they all were asleep--the strange old man, bony and tall, with goggle eyes and heavy glasses, the tall young man and the blonde girl. They all had berths forward. The captain and mate were aft; the native crew, below deck. There was no need for any of the crew, now. The boat was anchored. Only he, Johnny Thompson, was needed, to keep watch for prowlers of the sea, or signs of a storm.

It was strange, this new job. He was not sure just what these people were planning--some scientific expedition, he thought. The ship's outfit was rather irregular, but he had been glad of the chance to sign up as watch. He loved the sea.

"Someone--" he said to himself, "--is moving, up there." He started forward, cautiously.

He had covered only half the hundred and twenty-five foot length of deck when suddenly he beheld the girl of the party.

"Walking in her sleep," Johnny thought, with a touch of alarm. But she wasn't.

"Hello!" She poked a hand from beneath her midnight-blue dressing gown. "It's too swell a night to sleep."

"Yes," Johnny agreed.

"You're not a regular watch, are you?" she asked.

"That--er--" Johnny hesitated. "That's not my regular job. Nothing is. Does that matter?"

"No, I suppose not. Anyhow nothing could happen, here."

"Plenty could happen," he contradicted, quietly.

"How do you know?"

"I've been in the Tropics before. Natives get ugly sometimes. They imagine white men are getting the best of them--which, for the most part, they are!" Johnny laughed. "Then there are storms," he went on. "Wildest place for storms you've ever seen. Once I drifted before a storm for thirty-six hours in a boat just about like this, only--" he hesitated, "it was different."

"Yes," the girl laughed, "it must have been, as there's not another boat quite like this in all the world, I guess. It--

"Look!" she exclaimed softly, pointing toward the distant island. "What's that strange light?"

"Light?" Johnny spun round. "Oh! Say--that _is_ strange! It's green. A green light."

"Like an arrow," the girl whispered. "Green arrow of the Tropics. Quite romantic! But what can it be?"

"It's not for us," said Johnny. "It--it seems to blink. Wait!"

Retracing his steps he went to a box of life-preservers where he had left his heavy field glass. He returned quickly to her side.

"Now," he invited, "have a look!" He held the glass in position for her.

"It--it _does_ blink," she murmured. "It's like an electric sign. Some lights go off; others go on!"

"Let's see." Johnny took the glass. "Why--it's some sort of signalling," he decided at once. "But not for _us_!"

Instinctively they turned to scan the sea.

"There's no other boat out there," said Johnny. "At least there wasn't any at sunset. If one had moved in, we'd see the light."

"If there were a light," whispered the girl, "how gorgeously mysterious it'd be. How--

"Look!" she exclaimed. "Do you see it? A green arrow out there on the sea?"

"No--oo," Johnny said, after a moment of gazing. "I can't see it. Must have been a reflection of that other light. That often happens, you--"

"No!" The girl said, emphatically. "There! I saw it again!"

"Perhaps I'm color-blind," said Johnny after another long look. "But I just don't see it!"

At that he turned around to continue his study of that land light.

"It's strange," he murmured. "I can't quite count the lights, but they _do_ go on and off. Irregularly, too. It must be a signal. But what are they saying?"

"And to whom?" the girl added.

"Well," she sighed a moment later, "we'll not learn the answer, at least not tonight. Because it's gone!"

"So it is," said Johnny, after a long look at the island.

"Sha--shall we tell them?" he asked after a moment.

"Who? Grandfather and Dave? Oh--why should we? It can't be anything that affects us! Let's keep it for our own little secret. Perhaps we'll solve the riddle--"

"All right," Johnny agreed, readily. There's a queer girl for you, he was thinking. She'd be lots of fun, though.

"Is the elderly man your grandfather?" he asked.

"Yes. Professor Casper's his name. Only wish I knew as much as he does. My name's Doris--Doris Casper." She put out her hand. "I--I'll be seeing you. Good night. And don't forget--it's our secret--sign of the green arrow!"

She was gone.

"Sign of the green arrow," Johnny whispered, softly. "Perhaps I _should_ report it to the professor. And then again--perhaps I shouldn't. It can't have a thing to do with this boat, and it's entirely out of my line of duty. The girl wants to share a secret. Most girls do, in fact. So why not?"

With that, for the present at least, the whole affair was dismissed from his mind.

Half an hour later he found himself sitting alone on the after deck, glancing away at those dim, mysterious shores, and thinking back over the events that had led up to this mildly exciting night.

Two months before, he had found himself in New York wanting a job, and not able to find one. After three weeks of trying he had grown somewhat bitter about the whole thing.

"I'm intelligent," he had said to a prospective employer. "I've always worked. I like it. Why shouldn't I have a chance?"

"Why not?" the grey haired man had replied sadly. "I've asked that question often, but I don't know the answer. I only know we can't use another man."

That very afternoon, while watching boats moving out to sea, Johnny had his chance, and took it. He caught sight of a young man, struggling toward a gang-plank under a heavy load.

"Give you a lift?" he had volunteered, courteously.

"Whew! Yes." The man mopped his brow. "Looking for a dime?"

"Not yet!" Reddening, Johnny impulsively jerked a few small bills from his pocket. "Not broke, yet."

"Oh!" The man looked at him with interest. "Say!" he exclaimed. "I shouldn't wonder if you'd do!"

"For what?" the boy asked.

"I'm off to the Spanish Main to take pictures--native life, ancient ruins, and all that. There's a lot of stuff to lug, and--" he hesitated, "perhaps a fight to step into now and then! Want to go?"

"_Do_ I?" Johnny grabbed the two largest bags.

"There's no money in it! Just experience and expenses."

"All right! What are we waiting for?" Johnny led the way up the gang-plank.

All that had been two months before and what wonderful months those had been! Sailing from island to island, they had taken pictures of quaint, native homes, of native women with flashing eyes, of ancient buccaneer cannon, fast rusting to nothingness. There had been three exciting fights, with men who had thought they were intruding. In one of these, a machete had come within a fraction of an inch of Johnny's ear. He seemed to feel the cool swish of it now.

Then, he thought with a sigh, those golden days had ended. Lee Martin, the photographer, had been called back to New York.

"You keep the stuff," Lee had said to Johnny. "You may be able to get some unusual pictures. If you do--send 'em home to me. I'll see what I can make out of 'em, for you."

Johnny had watched Lee's boat fade into the distance. Then, with heavy heart, he had marched back to his lodgings in Port au Prince, the capital of the Island Republic of Haiti.

That very day he had noticed the _Sea Nymph_, located the man in charge, and signed up as watch. His photographic equipment was in his stateroom. He had laid in a good supply of film packs and plates. Would he find opportunity to use them? Would he get some unusual pictures to send to Lee Martin? Time was to answer all these questions in its own way....

"It's a strange layout," he thought, as he took a turn about the deck. "I suppose I'll know what it's all about before long."

It was indeed a strangely equipped craft. A three-master, with an auxiliary motor for bad weather, the _Sea Nymph_ had been built for island trade. Since the bottom had dropped out of the sugar market, she had been lying idle in the harbor. Without making many changes, the elderly professor had equipped her for his purpose, whatever that might be. Johnny had not yet been told. There had been a hold at the boat's center, for sugar and other freight. This had been transformed into a tank--or swimming pool. Johnny could not tell which. Doris, garbed in a gay swim suit, had taken a morning plunge there, but he had a notion it was for some other purpose, also.

Strangest of all, close to the stern where it could be reached by the stout hoists, was a large, hollow steel ball. It was all of eight feet in diameter, and its walls were several inches thick. What, he had asked himself more than once, could that be for? But he had asked no one else. The natives would not know, and one simply did not ask such questions of an employer. Besides, Johnny had learned long before, it is a waste of time to ask questions which, in good time, will answer themselves....

CHAPTER II SPOOKY WATERS

Johnny's questions regarding the steel ball were answered the following afternoon. After his usual six hours of sleep, he was sitting on the deck when the young man they called Dave--his whole name was Dave Darnell--approached him.

"I saw you taking pictures yesterday," Dave said with a smile.

"Yes," Johnny answered. "Just a picture of that island. I hope you didn't mind."

"Not at all", said Dave. "That looked like a rather good camera."

"It is!" Johnny exclaimed. "None better. Of course," he added, grinning, "it's not mine. It was loaned to me. And there's equipment, screens for infra-red pictures, flash bulbs, flood-lights--about everything."

"Say--ee--" Dave exclaimed. "Looks like you're a real find! Want to go down and try your luck at taking pictures?" He nodded toward the big steel ball.

"Down?" Johnny asked, a little blankly.

"Yes--to the place of eternal night!"

"E--eternal night!"

"That's right! I can't describe it to you! But I can show you. Question is--can you take pictures in complete darkness?"

"They don't come too dark for me!" Johnny flashed back. "Lee Martin and I took a picture of a Voodoo witches' meeting--people hiding in the dark from the island police. You couldn't see your hand. But we got the picture all right. And I nearly lost an ear! A burly black fellow swung at me with a machete!"

"Nothing like that down there," Dave chuckled. "All the same--you'll be surprised! Do you want to go?"

"Sure--I'll go," Johnny agreed. "Only," he hesitated, "I have a strange horror of being completely out of touch with the rest of the world! What do we do about that?"

"That's easy!" Dave laughed. "We have a short-wave set on the boat and another in the steel ball. Doris or the professor is always listening in. How about it--do we go?"

"We sure do!" Johnny grinned.

"O.K.! Get your stuff together. We'll go down in an hour!"

"Wonder what I'm getting into now?" Johnny asked himself as he walked to his stateroom.

An hour later he found himself passing through one of the strangest experiences of his life. He was seated, doubled up. Had he wanted to stand, he could not have done so. His eyes were wide open, but he saw never a thing!

"Inky black!" he whispered.

"Nowhere else will you see such darkness," came Dave's voice, close at his side.

"But look! There's something!" Johnny exclaimed in a low tone.

"Yes!" Dave's voice rose excitedly. "And it's something quite new!"

Johnny stared with all possible intensity. Before him--how far away he could not tell--there moved a series of small, round spots of yellow light. "It's like flying through the air at night," he murmured; "and seeing the lights of a huge Zeppelin passing."

"Quick! Get your camera ready!" said Dave.

"All right--it's all set!" Johnny's own voice sounded strange to him.

"I'll turn on the light," said Dave. "Now!"

"One, two, three--" Johnny counted to ten, and closed the camera shutter with a click.

"Now! One more picture," urged Dave. Another click. "They're passing. They'll soon be gone. If only it works!" Dave's voice grew louder with excitement.

"There", Johnny sighed. "That's two pictures--I hope!"

"No time for another," said Dave.

Johnny stared once more at the blue-black darkness before him, and marveled afresh. Could anything be stranger than this? Queerest of all--there had not been one ray of visible light. And Dave's voice at his side had said, "I'll turn on the light!"

But Johnny knew what it was all about. He had taken pictures in the dark before. Still the strangeness of it all, baffled him.

As if brought on by the darkness and mystery, he suddenly thought of something he must tell Dave.

"Samatan is stirring up trouble with the crew of the _Sea Nymph_!" he said.

"Our cook? Samatan?" Dave's voice registered surprise. "You must be mistaken."

"No" said Johnny. "I heard him last night".

"But why should he? He is well paid."

"That's what I don't know." There was a note of perplexity in Johnny's voice. "It's what somebody must find out. What if he should persuade the men to hoist anchor and sail, _right now_?"

"Right now?"

"Yes."

"That would be practically fatal! It--

"But look!" Dave's voice changed. "There they are again! I never saw such a sight! Get ready for another picture!"

Johnny quickly took another picture--two--three more pictures. After that, the spots of yellow light disappeared as before, and--for what seemed a very long time--there was nothing but inky blackness.

Johnny settled back for a few, fleeting thoughts. That he was due for some unusual experiences he had never a doubt. Fancy, going far beneath the surface of the sea in a thing like this steel ball! Suppose something went wrong--even the least little thing! What then? Dave had told him it was possible to go down half a mile, perhaps more. Would they ask him to go down that far to take pictures?

Sometimes, he thought, it's better not to know too much about what is ahead.

He had been vastly interested in their manner of taking off in that steel ball. They had crawled through a small entrance in the side, and taken their places. Then had come the bang of a steel door, swung into place. This was followed by the clang of wrenches, bolting them inside!

Dave had seen him move, restlessly. "Don't let that bother you," he had laughed. "I've been down scores of times. It--it's just grand! Professor Casper got the thing up," Dave had explained. "Now his doctor won't let him go down--on account of a bad heart. So it's up to me, on this trip. There are things we want to know. Your pictures should help."

There hadn't been time for any more talk. After the door had been securely bolted down, the hoist had lifted them over the rail and lowered them gently into the inky depths.

With a suddenness that was startling, Johnny awoke from his revery. Like the flash of electric bulbs, lights were appearing and disappearing before his eyes.

"Wha--what is it?" he exclaimed.

"Shrimp," was Dave's matter-of-fact reply. "Something is after them. The squid shoots out ink to make himself invisible, but in this darkness that would do no good. These shrimp shoot out little balls of fire. Look!" Suddenly Dave switched on a powerful electric light, and the little world about them was transformed.

Seeming to swim in air, a score of tiny, crab-like creatures moved rapidly across the spot of light. Viewed through the six-inch-thick window of fused quartz, they seemed fantastic indeed.

For a few seconds the space before them was a dark and empty void. Then again, it filled with darting creatures. Dave switched off the light, and once again the shrimp disappeared. As soon as the more powerful light from their strange, sub-sea visitor had been turned on, they had appeared as dark, darting creatures.

"What was following them?" Johnny asked.

"Who knows?" There was a suggestion of deep mystery in his companion's tone. "That's the thrill and charm that comes from exploring the sea's depths! Anything may put in an appearance. Creatures such as the world never has dreamed of, may pass before our eyes!"

"How strange! How sort of--"

Johnny broke off to stare, then to exclaim--"There--there's something _huge_!"

"Quick! The camera!" Dave's voice trembled. "No--it's too late!"

Moving with surprising swiftness, some great, dark bulk passed through the outer edge of their narrow beam of light.

"Wha--what was it?" Johnny felt a little giddy.

"Some huge creature of the deep. Perhaps a whale or a black fish," Dave replied quietly. "It is known that they penetrate to these depths. Then again--perhaps it was some huge, scaly creature that inhabits these depths alone."

"What if it had collided with us, or tangled in our cable?"

"Then," Dave's tone was dry and droll, "we might have taken a long, swift ride through space!"

"Swinging like a pendulum?"

"That's it! On our thousands of feet of cable."

"I shouldn't like that," Johnny shuddered.

"Then why bring it up?" Dave chuckled.

"Why, indeed!" Johnny laughed--

After another half hour of waiting, for one more fascinating spectacle, Dave decided to signal for their return to the top. Johnny experienced a real sense of relief.

"To explore the depths of the sea--earth's last great frontier--this is our purpose," Dave said, as they began to rise. "For centuries men have been discovering strange creatures washed up on beaches. They could have come from nowhere save the ocean depths. For many years they have been dragging these depths with nets, to discover, if they could, what lived in these 'spooky waters' of dense darkness."

And now, Johnny thought exultantly, I am having a part in an expedition that may reveal the secrets of these dark depths.

But once again his mind returned to Samatan. This strange person, with his apparent hold on the native crew, was cook for the expedition. And a marvelous cook he was. Johnny had been interested in the strange old man, from the first. He had studied him carefully. And there could be no mistake about it--Samatan was endeavoring to stir the crew to something....

Now the blue-black world about him appeared to be changing color. The blackness was less intense.

"It's like the coming of dawn," he said to Dave.

"Yes," Dave chuckled, "only here we may make our own dawn, slow or fast, as we choose!"

That this was to be rather a fast dawn, Johnny was not long in discovering. But it was fascinating. To pass from inky blackness to dark, deep blue, on into colors that resembled a sunrise, and then to the eternal blue of a bright, tropical day, was an experience not soon to be forgotten. From time to time as they rose, strange denizens of the sea seemed to peer at them. Once a shark shot past, and just before they reached the top, a great turtle swam awkwardly away.

Came the bump--bump of their steel ball as, lifted by the great crane, it landed on the deck. Then, almost before he knew it, Johnny thrust his head into bracing fresh air, to be greeted by a smiling face and to hear a girl's voice saying:

"Hello, Johnny Thompson! How do you like being down in Davey Jones' locker?"

After assuring her of his enthusiasm, Johnny hurried to his stateroom. He was wondering whether Doris remembered their "secret" of the night before.

CHAPTER III A BRIGHT EYED BEACH-COMBER

Johnny went at once to a darkroom that had been quickly prepared in the hold. Pictures could be taken on land in what appeared to be complete darkness; he knew this from his work with Lee Martin. But would the utter blackness beneath the sea be the same? He would know, soon.

He watched the films with absorbed interest. As the developer took hold, he saw nothing but blackness.

"Nothing there!" he muttered disappointedly. "Wasted shots. We--"

But wait! Was something coming out? Yes! There it was! An indistinct, shadowy form!

His thoughts leaped ahead. His pictures were to be a success. He would be asked, times without number, to go down in that darkness and take more pictures. Dangerous work, but he had to be a good sport, and besides, it was splendid experience for him.

The strange, undersea creatures, some very large, with heads as long as their bodies, with fantastic buck teeth and hideous eyes, some small and snakelike and some as normal looking as any fish to be found near the surface, came out clearly visible on the film.

"Perfect!" was the professor's enthusiastic reaction when Johnny showed him damp prints a few hours later. "A real contribution! And you took them in complete darkness!"

"In what appeared to be complete darkness," Johnny corrected. "I did it with an infra-red light screen. That screen shuts out all but the infra-red rays. Eyes can't see the light of these rays.

"Of course," he went on, "we might have used a flood light, but that would have frightened those creatures away. As it is, we got them in what you might call a natural pose. Candid camera shots from the deep sea," he laughed.

"Yes, yes," the professor agreed. "Very remarkable and most useful!"

"Of course," said Johnny, with a touch of modesty. "I learned all this from Lee Martin. He took me on as a helper and sort of body-guard. I just absorbed this camera stuff as we went along."

"I see," said the professor, "that you have learned one of the real secrets of success."

"What's that?" Johnny asked.

"To learn all you can about everything that comes your way, and to file that knowledge away in your brain. One never can tell when the opportunity to use such information may come to him. Perhaps never, but it's always there!

"You should be a great aid to us," the professor added thoughtfully. "You see," he said, leaning forward in his chair, "I regard this work as the most interesting and exciting of my entire career. Young man,"--his eyes fairly shone, "what place do you think of as our last frontier?"

Then, before Johnny could reply--"You may go east, west, north, south" the professor continued "but you find no frontier. You must go up or down! Up into the stratosphere--or down, into the sea. These are our last frontiers. Dave and I have chosen the deep sea, because there we may yet discover forms of life not known to man. These pictures," he held them up, "show two types of fish never before seen--and we have but begun!"

* * * * * * * *

"We have but begun," Johnny repeated softly to himself as, some hours later, he once more paced the deck in his solitary vigil. "We have begun. Where shall we end? We--"

His soliloquy was interrupted. Had he caught a gleam out there on the water? He thought so. Now it was gone.

That was one thing he was to watch for--natives in dugouts and canoes. Who could tell what they might do? In a strange land one did well to keep close watch. He would keep an eye out for that light....

"Exploring our last frontier," he whispered softly. He was in for something truly big again. Big, exciting, and dangerous! Well, that was the life. Life, action, thrills--and a touch of romance! Boy-oh-boy! That was the stuff!

But there _was_ a gleam of light on the water! There could be no mistaking it. It was closer, too. What should he do? Call someone? After a moment's thought he decided to wait. His flashlight would reach out a hundred feet or more. Time enough when those people, whoever they were, came within reach of his light. So, somewhat excited, Johnny waited by the gunwale, watching the bobbing of a tiny light--now here--now there--now gone--but ever coming nearer.

He waited, breathless, tense, expectant, watching for some craft. What would he see? Dark faces? Gleaming spears? Flashing machetes? Soon he would know.

When at last he cast the gleam of his powerful light on the spot where that golden glow had last shown, he gasped in astonishment.

"A girl!" he exclaimed, amazedly.

Yes, it was a girl. In a dugout patterned after a white man's canoe, she came straight on, without a sound. Her boy's shirt and blue slacks were faded, but clean. Her reddish-golden hair fairly gleamed in the light. She had a round, freckled face and smiling eyes.

As she came alongside, Johnny reached over, took her line and made it fast. Then he gripped her small, firm hand and helped her over the low rail.

"I--I had to come," she breathed. "I--I've been watching you for days. What--" there was tense eagerness in her voice, "what is that big ball you let down into the sea?"

"That," said Johnny, after bringing her a deck chair, "is for going down, down, down, to the bottom of the sea!"

"I--I hoped it would be."

"Why"

"Our trading schooner, the _Swallow_, sank. We--we can't find it. I thought--"

"Thought these people might find it for you?"

"Yes! Yes--that's it! Do you suppose--"

"I can't tell about that. You see," Johnny hesitated, "I'm only a watch, on this boat. I--well you might say I'm just a tropical tramp!"

"That," said the girl, putting out her hand, "makes us kin! Grandfather and I are beach-combers!

"You see," she went on, after giving Johnny's hand a quick grip, "I sort of ran away from home. No, not quite that. I was half through college. It cost an awful lot. My folks couldn't afford it, but they wanted me to finish anyway. I wouldn't let them spend the money, so I asked grandfather to send me a steamship ticket. He did--and here I am! It's grand! Really gorgeous! These nights." She spread her arms wide. "The jungle! The water rushing along the shore, the birds, the flowers, romance, adventure, everything! It's just grand!" Her face fairly shone.

"But our boat," her voice dropped, "sprang a leak in a storm. The natives were sailing her. They lost the location and we can't find it. Perhaps--"

"You'd have to see Dave," said Johnny.

"He's the young man who goes down in the steel ball? I--I've been watching you through the glass."

"Yes, that's Dave. He takes his work of exploring the sea's depths very serenely! Tell you what!" Johnny exclaimed. "You get him to take you down!"

"In--in that thing?" The girl drew in her breath sharply, eyeing the distant shadow of the huge sphere.

"Sure, in the steel ball! He'd like to! He's proud of it. And he likes showing people strange things. If you want someone to do a certain thing for you--ask him to do something else, first! That's a grand rule." Johnny looked into the girl's frank, grey eyes, and decided he liked her.

"Yes--I--I suppose so," the girl replied, slowly. "But you know--well, anyway--it's worth thinking about!"

"Look!" said Johnny, starting up. "Perhaps you can tell me what _that_ is." He pointed to the distant island, where again the blinking green arrow could be seen.

"No, I--" The girl sat there, staring. "I never saw that before. But you know," her voice dropped to a whisper, "there are spies on these islands! Lots of spies!"

"Spies?" Johnny's voice expressed astonishment.

"European spies," she added.

"But why?"

"I don't know about it. Grandfather can tell you all there is to know. He's always talking spies, and saying what they'll do when the time comes.... You must come over and see us. Our place is just over there on the shore. You'll come, won't you?"

"Yes. Certainly I'll come."

"Thanks a lot." Once more she gripped his hand. "And now--goodnight. I--I'm glad I came." She was over the side and away.

"Well, I'll _be_!" said Johnny as he settled back in his chair. A moment later, faint, and far away, he heard her voice come over the dark water:

"My name is Mildred Kennedy. Be sure to come see us--don't forget!"

For answer Johnny whistled once, cupping his lips with his hands, to reduce the likelihood of arousing anyone on board. After that he was left to silence and the night--and the mysterious arrow of green light, blinking away on the distant hillside.

Sliding out the field glass, he studied that arrow for two full minutes. He felt sure from its strange blinking and winking that it was being used as a code signal. For the life of him, however, he could not make the lights separate themselves. They always remained a blur.

"Too far away," he grumbled. He wanted to hoist anchor and let the boat drift closer to shore, but this, he knew, would not do. He was neither skipper nor mate.

Suddenly recalling Doris' words of the previous night, he realized that he had made the light, the secret of the bright-eyed little Mildred Kennedy! "I won't tell Doris about that!" he decided. "At least, not yet."

He was seized with a sudden desire to know who was receiving those blinking signals of the green arrow. Deep in thought, he turned his back to the island and, to his utter astonishment, saw above the motionless sea some distance away, a second blinking green arrow!

"Ah!" he breathed, lifting the glass to his eyes. Digging into a pocket, he dragged out a pencil and a small notebook. After that, for fully ten minutes, he held the glass with his left hand while setting down numbers. 5 - 7 - 11 - 9, 13 - 6 - 3, 4 - 9 - 2 - 7. He wrote down figures and more figures, until a strange, rushing sound reached his ears.

Startled, he sprang to his feet. On the shore side he saw a broad band of white foam rapidly approaching the boat. Standing there, mouth open and staring, he watched it sweep toward him. With a hissing roar it swept beneath the boat and, without causing the least movement of the craft, went rushing on.

"False alarm," he murmured. "Probably what they call a rip-tide."

Turning back to sea, he looked again for the blinking green arrow. But it was gone. The distant island hill, too, now was entirely dark.

"Strange," he muttered, as again he paced the deck.

And indeed it was strange, for the ship's log had recorded no boat in sight at sundown!

From then, until Johnny's vigil ended with the dawn, there was nothing to disturb the calm stillness of the tropic night.

CHAPTER IV SPIES

On board the _Sea Nymph_ was a small boat known as the Tub. Very short and broad, it rowed like a washtub, and in a storm, would have been about as safe as a laundry basket. But water held no terrors for Johnny, so, late the following afternoon, he pushed the Tub into the sea and headed for shore.

"You came! How grand!" Mildred Kennedy came racing down a palm-lined path to greet him.

She wore an orange-colored smock, and there was flour on the hand she held out in greeting.

"I'm making cookies," she confided.

"Sounds great!" Johnny grinned.

She led him to a broad, screened porch where a bearded giant unwound himself from a deep, comfortable chair to meet him.

"This is grandfather." Real pride shone in the girl's eyes. "He's been a beach-comber for thirty years. That's a record!"

"Now, child," the old man drawled, "don't you go bragging on me.

"Have a chair," he directed Johnny.

"My cookies will burn. I'll have to hurry," said the girl. "Grandfather--you tell him about those spies."

"Spies? Oh, yes. Those European fellows." The old man's face darkened. "I've been preaching against 'em for mighty nigh twenty years. Mebbe longer than that, I reckon. You see, Mr. Thompson--"

"Please call me Johnny," said the boy. "I'm not used to the 'Mister'."

"All right, Johnny. That's what it shall be. You see, Johnny, these islands were once a French colony. The French made slaves of the natives. They brought in a lot more slaves and before long, there were many more slaves than there were Frenchmen. So the natives polished up their machetes, started poundin' their Voodoo drums, and drove the Frenchmen off the islands. This has been a republic ever since.

"But spies, now," his voice dropped. "How'd you get to thinkin' o' spies?"

"Your granddaughter told me there were spies. And there's been a green arrow--an arrow of light--on the hill at night, and another on the water. It's sort of mysterious."

"A green arrow of light," the old man repeated. "That's what Mildred was telling me. Strange that I never saw it."

"You couldn't," said Johnny, "unless you were on the water. It's near the middle of the island, and up high."

"There's a place up there built of stone, half castle--half prison," Kennedy said, thoughtfully. "Some Frenchman built it, thinking he could hold out against the natives. Well, he couldn't, and now the natives think it's haunted. Won't go near it. It's a long way up a terrible trail.

"But those spies, now," he added thoughtfully. "They may be using it for a hideout and signal tower. They stop at nothing."

The old man rose, circled the porch like a prowling tiger, then returned to his seat.

"These natives," he went on, "are a simple people. They can't run a country. They found it out soon enough. So did these other people, these Europeans. I won't name the country as you'll learn it soon enough. Those Europeans came here and began boring in, just as they do everywhere. You'll find them in every South American republic and every island of the sea. They're robbers, spies, traitors!" His voice rose. "They rob the people, and at the same time plot the overthrow of all governments but their own.

"Young man!" Mr. Kennedy left his chair with surprising vigor. "Did you ever take a good look at the map, and think how important this Caribbean Sea is?"

"No, I--"

"Come here. Have a look!"

They stood before a large wall map. "Look at it," Kennedy insisted. "Plentiful islands with Central America on the west. A score of wonderful harbors. Suppose those people took possession of these islands. Look at Haiti! A harbor where an entire navy might drop anchor! Yes--and room left for ten thousand seaplanes! Bombers! How would our Atlantic coast--Miami, Charleston, New York, Boston--how would they look, after those planes had been raiding from this base for a week, if there were war. And who says there _won't_ be!

"You saw a light on the water!" He whirled around.

"Yes! Low down! A green arrow of lights, that flashed."

"'Low down'!--I should say they were!" The old man grimaced. "Spies!" he muttered. "Since our Marines left the islands--we took control during the World War, you know--these islands have been nests of spies! Something should be done about it. But these natives sleep on--and Uncle Sam doesn't care to interfere. And yet I'm beginning to hope he will--before it is too late!" His words trailed off as he resumed his seat.

"These people may call themselves beach-combers," Johnny thought to himself. "Perhaps they are, in a way! But they're grand folks."

The house, which he presumed had been built with native labor, was made of massive, hardwood logs. There was no glass in the broad windows, but bamboo "screens," which could be let down at night. Mosquito-net canopies were hung over the beds to keep out insects. Most tropical houses are like that.

Behind the house were orchards--grapefruit, oranges, bananas. And down in the flat land by the shore, sugar cane was growing.

"We cut it out of the wilderness, the natives and I," the old man rumbled, in response to Johnny's polite inquiry. "They're quite wonderful, these natives--once you come to understand them.

"Of course," his brow darkened, "some of them can't be trusted. Those men, those Europeans--" his tone was bitter, "have corrupted them. Yes, and robbed them, too! They pay little for their produce, wild rubber, chicle, wild coffee. And they charge the natives high prices for cheap goods. They get the people deeply in debt to them, and then make slaves of them.

"That," he sighed, "was why we bought a trading schooner, Mildred and I. We wanted to give the people of our small island a chance. We were doing it, too!" He struck the table a blow with his massive fist. "By George! We were doing it!

"But our boat's on the bottom now!" His voice fell. "Our natives took her out in a storm, and she sprang a leak."

"Yes, I know. Mildred told me." Johnny was wondering whether some treacherous native, inspired by the Europeans, had let the water into the Kennedy boat. At the same time he was making a resolve to do all he could to find the boat and help bring it to the surface.

Mildred entered with a great plate of cookies and a pitcher of ice-cold, fruit juice.

"I hope you like them," she smiled.

Johnny did like them. What was more, as the moments passed he became more and more interested in his new-found friends. They were, he told himself, good, kind, intelligent people--his kind. They would do things, together. He saw himself with the girl, following obscure trails in search of that spy castle whence, perhaps, the green arrow messages came.

"Well," he sighed at last, "I'll have to be getting back. It's been grand, this visit. I hope you'll let me come back, and that--that we can do things together." He was looking at the girl.

"Do things? What, for instance?" Her face was serious.

"Lots of things. Things that may help." He gave her a broad smile. Then--"just a big batch of day-dreams, I guess."

At that he shook hands with the old man, walked down the broad path with the girl, gripped her hand for an instant, then climbed into his Tub and rowed away.

"Thanks for one grand time," he called back.

"You're welcome, and thanks for coming," was Mildred's answer. And the hills echoed back, "thanks--thanks."

CHAPTER V WHISPERING DEPTHS

Johnny had an active mind. Figuring and planning were almost continuous activities with him. Sometimes he really tried to slow the process up, but his mind would keep right on, figuring and planning.

As he rowed slowly back to the boat, his thoughts were particularly active. There were things to be done. He would see that they _were_ done, in the end; he surely would. By going down in the steel ball as many times as Dave wanted him to, and by taking pictures, he'd put Dave in debt to him. Then he'd persuade Mildred to go down in the steel ball. Dave would like that. Then, at just the right time, he and Mildred would ask Dave to help find that trading boat at the bottom of the sea, and to float it once more.

Then they would get busy on those spies, he and Mildred and--and anyone else who would help. It was a patriotic duty, by thunder! It surely was! In his mind's eye he saw the map of the Caribbean Sea, these islands at one side, the Panama Canal on the other. If the Europeans got these islands, what would happen to the canal? Filled with rocks and mud--that was the answer! They'd bomb the very daylights out of it. Yes, they must uncover those spies--at least some of them. He wondered whether the green arrow would show tonight, and whether he would be able to make any sense out of the numbers he had written down in his notebook.

"It's some sort of code," he told himself repeatedly. "If I can decipher it we may get somewhere."

But here he was alongside the _Sea Nymph_, and Dave was saying:

"Hello, Johnny. We're shifting our position tonight--coming in a little closer. Tomorrow afternoon I'd like you to go down with me to get some pictures. You won't mind, will you?"

That was exactly what Johnny had planned. "No, I won't mind," he said, "that will be keen."

A mist drifted out over the ocean. All that night Johnny paced the deck in a chill fog. No green light showed from the island hills. Once he thought he heard men's voices, but nothing came of it. He was glad enough when he could crawl into his berth, draw his blankets over him, and lose himself in sleep.

When he awoke the sun was shining. It was mid-afternoon, and Dave was waiting for him to appear, for their trip below.

"What a life!" he murmured. After he had gulped some hot coffee, hurriedly bolted some seabiscuits and a piece of pie he reappeared on deck.

"All ready?" Dave asked.

"Soon as I get my camera and things."

"Good! I'll have the steel ball in shape P.D.Q.," Dave grinned, good-naturedly.

"He's really a nice chap," Johnny thought. "Only he takes science and discovery pretty seriously. I suppose we'll discover some saber-toothed viper fish, or maybe some flying snails!" He smiled at his thoughts. Life was not half bad after all.

Half an hour later he was experiencing such thrills as only the deep, deep sea could bring. Some five hundred feet beneath the surface of the sea he sat doubled up in his place, staring at an ever changing panorama. A rocky wall, not twenty feet from him, stood up like a sky-scraper, straight and tall. Here and there it was broken by fissures and caves. Everywhere it was festooned with sea vegetation--seaweed, kelp, anemones. All these, with coral that rose like Gothic architecture, were entrancing.

Dave was by his side--not to admire, but to record. The look on his face was almost solemn. As they moved slowly downward Dave spoke into a small microphone and Doris, up on deck, recorded his words. Strange words they were, too: "A school of parrot fish; three hatchet fish; two round-mouths; a golden-tailed serpent dragon; a--oh--oh!--Hold everything!"

At that instant Dave's window was opposite a dark cavern. As he threw on a more powerful light he caught the gleam of two, great eyes. How far apart they were!

Despite his efforts to remain calm, Johnny's heart skipped a beat as, at Dave's command, he touched his moving-picture camera and set it recording. What sort of creature was this? A whale? A blackfish? Or some strange, unknown denizen of the deep? Suppose at this instant it should become enraged, should rush out of its hiding place and drag the steel ball out into the deep--to send it crashing against the rocky wall? A broken window would mean instant death. And yet Johnny's hand did not tremble as he adjusted his camera....

Just after the steel ball had gone over the side, Mildred Kennedy, in her dugout canoe, had arrived for a visit. It had called for real courage, this little journey. From a distance these _Sea Nymph_ people had seemed so serious. All but Johnny. "But it's not decent to stay away and not be properly sociable," she had told her grandfather. So here she was.

There had been time only for a brief word of welcome from Doris. After that, whispering excitedly--"Dave and Johnny are below in the steel ball. It--it's dreadfully thrilling, even here on deck," Doris had clamped a pair of head-phones over her guest's ears and had whispered tensely:

"Listen!"

So they were seated on the deck of the _Sea Nymph_, listening intently for reports from below. At the same time, they talked.

"I came to visit my grandfather," Mildred said, "just as sort of a lark. I was storm bound indoors for two weeks, and when I saw how simple and kind the natives were, the happy, free life they lived, and yet how many things could be done for them, I wanted to stay. So I just did. And I am glad. Only--" A shadow passed over her face.

"Listen!" Doris held up a finger. "Thought I heard a whisper. It--it couldn't be Dave! I--I hope nothing has gone wrong. It's truly dangerous being down there, and yet one does learn so much--"

"Shish!" Mildred held up a finger. "I--listen--I hear a whisper! It--it's numbers he's saying. How strange!"

As the two girls sat in silence, pressing the phones to their ears, listening with their every sense, they caught--in a low whisper:

"Two hundred--and--eight--and a half. Ten. No--now a drop--thirty, thirty-one--two--three--"

Then Dave's voice boomed through, drowning out the whisper. "O.K. We saw some sort of monster," he was saying. "He was in one of these caverns and Johnny got his picture--we hope! Wish you were down here."

"So do we!" Doris' voice exclaimed. "We heard a whisper. Thought you might--"

"You've been dreaming!" Dave boomed back. "Forget it--and tell that man at the cable to let us down again, slowly. Boy!--how I do want to see things!"

Yes, Dave wanted to see things. Most of all, on this particular day he wished to go down--down--down into the watery depths, to discover, if possible, just how far down, sea vegetation and coral were to be found.

"If only I don't find bottom too soon," he thought. "And if the sea remains calm."

The sea. He shuddered a little at this. If the anchors held--all would be well. But if they should give way--that would be truly terrible. To the right and left of them, not a quarter-mile apart, were parallel walls of rock. To be dragged against one of these--? Who could tell what disaster might result!

* * * * * * * *

In the meantime, as they listened, the two girls talked of many things, of home, of thrilling tropical nights, of Mildred's sunken schooner and many other things.

Of a sudden, their conversation was interrupted by a sound, conveyed through their head-phones.

"Sh--"--Doris' hand went up. "It's that strange whisper again!"

"Whispering waters!" Mildred murmured. "How mysterious!"

Low as her tone was, the whisperer apparently caught it, for--still in that hoarse whisper--there came back:

"So we are mysterious! How very grand! And it was a lady who spoke!"

Once again Dave's voice broke in upon the whisperer: "Doris!" Tenseness was evident in his tone. "Doris!--Tell them to hold us right where we are!"

"_Hold it!_" Doris called to the windlass man, instantly.

"_Hold it_," came back the quick acknowledgment.

"All this," Doris said to Mildred, "is most provoking. You are just dying to know what strange things are happening below, what marvelous discoveries are being made--but the only part you have in it is listening and waiting!"

Down in the steel ball, Dave had caught a movement to the right, away from the cliff. Switching his light in that direction he had discovered a huge, dark object moving slowly through the water.

"It's that 'thing'!" he told himself. "The very thing I've seen before!"

To his great disappointment, the form was as indistinct as before. That it might be a whale he knew quite well. He suggested the idea to Johnny.

"But it's not a whale--I'm sure of it!" Johnny whispered. Swinging his moving-picture camera into range, he managed to catch the rear half of it before it passed from view.

"The camera sees more than the eye," he murmured. "Here's hoping."

Dave turned again to his task of exploring the under-sea wall. He signalled their continued descent.

A moment later the ear-phones on deck were silent. Both Dave and the mysterious whisperer were unheard.

"Who _could_ that have been?" Mildred asked.

"I've no idea," was Doris' reply.

"Do you know," Mildred added dreamily, "I have a feeling that whisperer was not far away!"

Doris started to speak but checked herself, suddenly. Once again she had caught the weird tones of the whisperer.

"One-eighty--eighty-two--eighty-six," he droned. Then he raised his voice above the whisper, and called:

"Hello there--you mermaids! Are you still there?"

"He _must_ be near us!" Doris exclaimed. "If not--why would he call us 'mermaids'?"

* * * * * * * *

At that same instant Dave was experiencing a thrill. Arrived at a spot opposite a broad shelf on the perpendicular wall, he and Johnny found themselves within five feet of the rock. Vegetation, which had been thinning out, was just disappearing.

And then Dave saw it--a long, wavering arm, reaching out for the steel ball. Involuntarily, he started back from the window. Then he laughed.

A second arm appeared. Then, a third.

"Octopus!" he whispered to Johnny. "Such a monster!" Instantly his light was on, and Johnny's movie camera was grinding away.

"Only one of his kind I've ever seen!" Dave was thrilled to the tips of his toes. "Wish he'd climb on board and let us take him up. He won't do that, but I'll get him, all the same! Some time I'll get him!

"How ugly he is! See how his eyes shine, Johnny! People sure would throng around him in an aquarium! Put him in with some gorgeous, tropical fish and you'd have a 'beauty and the beast' show! You--"

Suddenly he stopped speaking, to stare straight at the wall. They were moving away! There could be no doubt of it. Fascinated by the strangeness of the situation, he and Johnny sat motionless while the octopus faded from sight. Two yards--three--five--ten--twenty--they were swinging off! And behind him was a second wall, against which the window of the steel ball might crack like an egg shell.

At that instant Dave heard a strange voice repeating an idiotic question:

"_Hello there, you mermaids. Are you still there?_"

The very sound of a human voice seemed to rouse him.

"Doris!" he called. "The anchors have pulled loose! The ship is drifting!"

"_Hello, there_," called that same voice. "_So you're not a mermaid, after all!_"

Something had gone wrong with Dave's radio, Doris thought. His voice did not come through clearly.

"Hello! Hello Dave!" Doris called. "Repeat! What did you say?"

"_I said are you a mermaid?_" came in that teasing voice.

"Get off the air!" Doris stormed.

"Doris!" Dave roared. His voice came through clearly now. "The ship's adrift! Tell the captain to order our main anchor line played out--to pull hard to port!"

"Anchor line out! Hard to port!" the girl cried.

"Anchor line out. Hard to port!" came booming back the repetition.

Instantly Doris found her head in a whirl. Dave and Johnny were down a full thousand feet. On each side of their ball a rock wall rose high above them. To crash against it might mean disaster.

"Haul away--Top speed!" came in Dave's usual calm voice.

"Haul away. Top speed!" Doris called to the control man.

Complete silence followed. Even the "whisperer" appeared to have sensed the tenseness of the situation and had gone off the air.

That there was to be a race against time with their lives as a grand prize, Johnny realized at once. Here they were, several hundred feet down in the black depths of the sea, drifting at a fairly rapid rate toward a rocky wall. If they hit that wall? He shuddered at the thought. The pressure of water at that depth was tremendous. If the ball cracked, nothing could save them.

"Is there anything at all we can do?" he asked Dave.

"Not a thing, I guess," Dave answered. Then, "Yes! Yes, there might be, at that! There are the levers! They are _outside_ the ball and can be worked from _within_! I had them fixed up for gathering outside samples. If we lifted them into position, they'd lessen the shock if we hit the wall!"

No sooner said than done! Groping about, Johnny seized a handle here, another there, as Dave was doing. He felt much better when the outside levers were in position. They would provide a little protection, at least.

With astonishing speed, now, the wall approached. They could see every detail of the seagrowth clinging there. "Ten yards," Johnny guessed. "Eight--five--three--" He was sitting on the inner handle of the lever and gripping the other hard. "Now--now comes the test!" he breathed.

The words were hardly out of his mouth when there came a grinding impact that all but lifted him from his place. And then--they were free of the ledge!

"Free!" Dave cried joyously. "Doris! We are safe!" he called into his speaker.

The ball rose slowly above the top of the ledge.

Dave, however, had spoken too soon. Scarcely had he settled back when a great spiral of coral, like the towers of a church, appeared to leap at them. This, he knew, grew from the top of the ledge.

There was just time for a lightning decision, but they were prepared for it.

"This lever is closest," Dave exclaimed. "It's our window or the lever!"

Throwing their whole weight on the lever handle, they waited a second--two--three--ten--twenty. Johnny heard his watch ticking them off....

Then came the heavy jolt. He was thrown so violently that his head struck the top, and his senses reeled.

When at last he was able to sit up and look out, he murmured a fervent "Thank God." For the hazard was past. The glorious blue of water was all about them.

Fifteen minutes later the steel ball rested on the _Sea Nymph's_ deck. A few more moments and, hands first, like frogs leaping from a jar, the two tumbled out on the deck.

"Hel--hello, folks!" Dave said, standing up a trifle unsteadily. "How's the weather up here?"

"That," said Doris, gripping Dave's arm without realizing it and giving Johnny a happy smile, "that was awful!"

Mildred, gazing at them admiringly, echoed the thought.

"How about a glass of lemonade, and--and something to go with it?" Dave demanded. "Chocolate coated marshmallow cake, macaroons, and--"

"Dave, you'll get fat," Doris laughed.

"And then I wouldn't be able to get into the steel ball. Wouldn't that be grand?

"But no!" Dave answered his own question. "It wouldn't! Not at all. For I've been seeing things--wonderful things! And I'm going back tomorrow!"

After their little feast on deck, Doris accompanied Mildred to the boat's side, gave her a hand as she dropped lightly into her dugout, and said in a friendly tone:

"You'll come again, won't you--very soon?"

"Oh, yes!" Mildred exclaimed. "I'll fairly haunt you from now on, for we do get a little lonely--grandfather and I. But you must all come over and see us too! Won't you?"

"Oh, yes, very soon," Doris answered, cordially.

"Day after tomorrow is Sunday--how about then?"

"I'll let you know. It's up to Dave, really. He's so absorbed he almost forgets to eat. You see," Doris went on, "he's very fond of my grandfather, and wants to help all he can."

"These grandfathers of ours!" Mildred laughed.

Half an hour later Johnny came upon Doris, standing before an easel and putting the last touches on a picture of the sea, the island, and a gorgeous sunset.

"I didn't know you were an artist," he said in genuine surprise.

"I'm not," Doris frowned. "I only make a try at it. Those colors! You never can get them just right!"

"Looks swell!" Johnny said, admiringly. "Wish I could do half so well. Why don't you try an _underseascape_?"

"What would that be?" Doris wrinkled her brow.

"You go to the bottom of the sea, fifty feet or so down, in a diving helmet. You set your easel on the bottom, weight it down, and paint--whatever you see there!"

"Not really?"

"I read about it in a book. Found it in the ship's library. Anyway--it would be fun trying."

"Water would spoil your paint."

"It says not," Johnny grinned. "Only trouble is--little fish, like flies, get into your paint!"

"I'll try it some time," Doris declared. "I've been down twice with Dave. It's thrilling--walking on the bottom of the sea. Thanks for the idea, Johnny!"

CHAPTER VI REAL PROGRESS!

After going on duty that night, Johnny came upon Samatan, leader of the boat's native crew. He was seated in a corner, but one of the ship's lamps lighted his face. He was staring at the steel ball and there was unmistakable animosity in his expression.

"Looks as if he'd like to eat it," Johnny mused. "Wonder what it's all about."

A little later he heard the natives talking in their quarters below deck.

"Sounds as if they were angry about something," he told himself. More than once he heard Samatan's voice rising above the rest, as if he were making some sort of speech. He wondered if it could be possible that the European spies had somehow inspired these natives with hate for _all_ Americans.

"That would be bad," he thought. "It might spell disaster." He resolved to cultivate Samatan's acquaintance to find out, if possible, just what his grievance was. Then he might put things to rights.

Maybe some superstition is connected with the steel ball, Johnny reflected. When you are among primitive people you never know quite what to expect.

That night the green arrow blinked again. Johnny saw it, shortly after midnight. The boat was closer in, now, and he could make out the separate lights of the arrow as they flashed, up there on the hillside. If there was another light out at sea, it must have been far away--or too low to be visible. He caught no sight of it.

When the arrow appeared, Johnny got busy at once. With small circles, like coins in a row, he sketched an arrow, in pencil.

From the tip of the flashing arrow to the other end, there were thirteen lights. Besides, there were two lights slanting back on each side, at the tip. These four helped form the head of the arrow. Four others, in pairs, made the feather end.

As he watched intently through powerful binoculars loaned him by the professor, Johnny noted that the thirteen lights blinked separately, but the eight which comprised the head and feather of the arrow, blinked in unison.

"Those eight lights must stand for a period," he concluded. "The thirteen are letters, or code numbers. I wonder how they work."

For some time, as on that other occasion, Johnny recorded the winking and blinking of the lights. When at last the green arrow became dark, he took a turn about the deck, then settled down to the task of trying to figure that code. Dawn found him still figuring, but seemingly no nearer the solution.

"Dumb!" he exploded at last, as he crammed the notebook into his pocket and went to breakfast. When he returned to the deck late that afternoon he found Doris and Dave working over some notes.

"Hello, Johnny. How about those pictures we took yesterday?" It was Dave who spoke.

"Oh, yes," Johnny exclaimed. He had forgotten them. "Come on to the darkroom, if you like. I'll develop them right away."

Doris accompanied them to the darkroom. There, fascinated, they watched strange creatures of the depths come out on the film.

The great, shadowy creature which had peered out from a rocky cavern was, the picture revealed, a veritable deep-sea monster.

"If only I could bring him up!" Dave exclaimed. "But then, he'd never live at surface levels. But our great, sea-green octopus, I do believe, could live anywhere. I'm going after him!"

Most interesting of all--and most baffling--was the picture Johnny had taken of the great, slow-moving thing seen in the open water far from the rocks.

"Oh, that!" exclaimed Dave, as it began coming out in the film, "that's really a monster for you!"

"If it _is_ a monster," said Johnny, in a tone of mystery.

Whatever it might be, the picture only added to the mystery. Too far away, too indistinct to be seen clearly, the thing might have been a whale, or some other form of deep-sea monster. Truth was--deep down in his heart Johnny believed it to be neither. His theories were too fantastic to be put into words--at the moment.

* * * * * * * *

Their afternoon ashore the following day proved interesting, inspiring, and exciting.

They were served a grand meal of native wild turkey, baked sweet potatoes and all manner of delicious, tropical fruits. After that, Mr. Kennedy took Dave, Doris and the professor for a look at some unusual wild birds, nesting at the edge of the jungle.

Johnny settled himself comfortably in a split-bamboo chair and gave himself over to wondering and dreaming.

Mildred had gone to supervise the washing of her precious dishes--some of which dated back to ancient buccaneer days--so Johnny was alone with his thoughts. And strange thoughts they were.... He recalled having heard the bearded giant Kennedy saying to the professor--too much absorbed in research to pay much attention--"Those men, those Europeans! They starve their own people, and use the money to buy gunboats and cannon. They are slaves--those people--slaves! If we don't watch out _we'll_ be slaves, too!... Look at this Caribbean Sea! More important than the Mediterranean ever was! And who's to stop them from taking possession of these islands? Why, even the president of this poor little Republic is in debt to them! Up to his ears!"

Was Kennedy right? Johnny wondered, dreamily. What of that signal up there on the ridge--the signal of the green arrow? Was _it_ operated by spies? And if so--what had they been saying with those blinking lights? What--

"Penny for your thoughts!" Mildred was back.

"Not worth it." Johnny stood up. "Tell you what, though--I'll play you a game!"

"What sort of game?"

"Game of the Green Arrow. The object is to discover what it says!"

Drawing up a small table, Johnny spread a notebook and some papers on it.

"Now," he said. "Here's a drawing of the green arrow. Twenty-one green lights make the arrow. Thirteen in a row," he pointed out, "two here, two there, and two more on each side at the other end. The last eight blink all at the same time, but the thirteen--only one at a time. By their blinking they are conveying messages. But what do they say? Here's a set of papers with records of their blinking, all marked with numbers. If you can work that out, you go to the head of the class!"

"I see. Easy as that!" Mildred laughed, and promptly seated herself across from him.

After that, save for the lazy hum of bees or the sudden whir of humming birds' wings, there was silence in the place....

Suddenly the girl sprang up. "Why, I--I've got it!" she cried, excitedly.

"Just like that!" Johnny smiled.

"Well, I certainly have! Listen! This is what that first message says:

"_Keep a sharp lookout. There are counter-spies afloat._"

"WHAT! Gee willikens!" Johnny gazed at her, truly amazed. "How could you make it read like that?"

"Because that's the way it _does_ read!" she raced on. "It's really easy. There are twenty-six letters in the alphabet. Having thirteen lights suggests that they have split that twenty-six _in two_. Each light must stand for _two_ letters. But the question is--which two? Well, the _top_ thirteen stand for A, B, C, etc. But what about the bottom ones?

"The simplest way," she leaned forward, smiling, "would be to put the _last_ thirteen letters under the _first_ thirteen! Then, blinking _one_ light for _two_ letters, let the fellow receiving the message see _which_ of the two letters makes sense.

"I tried that," she went on "and it didn't make any sense at all, so I ran the _last_ thirteen, backwards. By trying each of the two possible letters in each instance, I got the message I just read to you."

"Which must be just about right," Johnny breathed. "Mildred--you're a wonder! Now let the old green arrow blink! We'll always know what it's saying--and we may make some startling discoveries." With that he seized her hands and whirled her wildly about the broad porch.

"List--listen," she panted, as, quite out of breath, she dropped into a chair, "what's that?"

"Natives singing, I suppose" said Johnny, "they are fond of singing."

"Those singers are not natives!" The girl held up a hand for silence. "They never sing like that. Besides--all those voices are men's!"

CHAPTER VII MYSTERY SINGERS OF THE NIGHT

Mildred was leaning forward, lips parted, listening intently.

"What are they singing?" she whispered.

"I can't make it out," was Johnny's slow reply. "Too far away. Besides--it doesn't sound like English, at all."

"Now," she said, softly, "now it is coming out stronger." A sudden breeze wafted the distant voices toward them.

"It's a funny old song," said Johnny. "I've heard it somewhere. Perhaps it's from light opera."

"But how strange to be singing that, here! Who could they be?"

"Who knows?" Johnny answered slowly.

"Now they're coming closer," he said a moment later. "Must be eight or ten of them!"

"Suppose they come all the way?" She gripped his arm firmly. "That would be--"

"I think we'll take care of ourselves, Mildred." His tone was deeply serious. "Some time," he added, reflectively, "we'll go up to that ancient castle that was a fort--and, perhaps, a prison!"

"We might, some day. Only--"

"Only what?"

"It might be dangerous."

"Poof!--What is danger?"

"I know. That's the way I feel, sometimes. What's the use of being afraid of--of anything?

"But we'd have to find the right trail," she added. "Those hills are terrible. They're all cut up with ravines. There are animal trails and native trails running everywhere. It--it's almost impossible to keep them straight."

After that, for a time, they were silent. The sound of singing, coming ever closer, increased in volume. The tunes changed, but not once could they understand the words. It was strange.

Somewhere in the jungle a jaguar screamed Nearer at hand some night-bird sang: "Oh--poor--me! Oh--poor--me!"

"It's dark," Johnny whispered. "Seems like the folks should be back?"

"They were going quite a distance, and anyhow they took flashlights."

To Johnny, the place suddenly seemed deserted and silent. Seeing a high-power rifle in the corner, he picked it up and threw back the catch. It was loaded. He set it back without a sound.

"There!" The girl's sudden exclamation startled him. "They've stopped singing! I expected that!"

"Why?"

"I don't believe they knew anyone lived here. I could tell all the time just how far they were, on the trail. I've heard natives singing over that trail a hundred times. The sound changes when they reach the clearing."

"And you think--?"

"I think that when they reached the clearing they were surprised. They didn't want to be seen. That's why they stopped singing. Now they must be going back."

"Or--coming on!" Johnny stepped to the corner and took up the rifle.

"No!" the girl's tone was decisive. "They've turned back."

A moment passed in silence;--two--three--four--five. Then the girl sprang silently to her feet.

"Come!" she gripped his hand. "Let's go have a look!"

Astonished, Johnny caught up the rifle and followed. Never had he known anyone who could get over a jungle trail so fast in the night. She carried a flashlight, but seldom used it. Three times she paused to listen. The third time, as Johnny stirred slightly in the path, she whispered:

"Shish!"

"Sounds like oars," Johnny whispered back.

"It _is_ oars!" came back in a barely audible whisper.

"Then they came by boat."

"Yes. Come on!" Once more she gripped his hand and this time they advanced slowly, cautiously. Not a twig snapped.

Once again they paused as a low, bumping sound reached their ears.

A moment more and they came out of the jungle, on a broad, sandy beach. Instantly Johnny's well-trained eyes swept the sea. The moon was just rising. It painted a golden path across the waters, far into the distance. But there was no sign of a boat.

"Can you beat that!" Johnny murmured, softly.

"We must have been mistaken," said Mildred, wonderingly.

"Only we were not!" Johnny thought. But he made no comment.

Gripping his arm, the girl led him along the beach until they came upon a mark in the sand.

"A boat was pulled up here," she said, positively.

Johnny threw a gleam of light on the spot. "Queer sort of mark," he murmured. "No regular boat! It's like the mark a white man's boat would make--or perhaps a collapsible boat."

A moment later his eyes caught a faint gleam. Pretending to examine the sand, he stooped over to pick up a metal disc. Without knowing just why, he thrust it into his pocket.

"What she doesn't know won't worry her," he told himself a moment later.

"Well," Mildred said, in a tone of forced cheerfulness, "this seems to be the end of the search. Let's go back."

"O.K."

They turned about and were soon threading their way back through the jungle. "Johnny," she said at last, "We need our boat more than ever, now."

"For protection as well as profit?"

"Yes."

"Ask Dave to take you down in the steel ball," Johnny suggested. "He'll do it, I'm sure, as he's in love with the professor's invention. Can't say I blame him, either. After that--ask him to help find your boat".

"I'll ask him tonight, if he'll take me down."

And she did.

"What's that?" Dave asked, as they all sat on the porch, a little later. "You want to go down in our steel ball?"

"Yes. Yes--I--I'd like to." The words took real courage, as she did _not_ want to. In fact--she was dreadfully frightened at the thought. And yet--

"Well," said Dave, "I don't see why you shouldn't--tomorrow."

"To--tomorrow?" She shuddered slightly, but he could not see her, in the dark.

"Yes, tomorrow. There'll be no picture-taking. I'm going after a sea-green monster--probably the largest octopus anyone ever saw!"

"Oh--o--o!"

"He won't get _you_," Dave laughed. "Can't get inside the ball. What do you say? Is it a date?"

"Yes--I--yes! Yes! Sure it is!"

"Fine! Can you be on board at eight in the morning?"

"Yes--I--I'll be there. Thanks--thanks a lot!"

"Well," she whispered to Johnny a short time later. "He's going to take me down! Tomorrow! And I'm scared pink!"

"You needn't be," Johnny laughed. "It's safer than an auto on Michigan Avenue in Chicago! And just think--you'll be the first young lady ever to go down five hundred feet beneath the surface of the sea! At least, I imagine you will!"

"That," she replied with a slightly unsteady chuckle, "will be a very great honor!"

* * * * * * * *

As Johnny changed to heavier clothes for his watch, later that night, the disc he had found on the beach, fell from his pocket.

He picked it up and realized instantly that it was a button from a uniform jacket.

"So that's it!" he murmured, as he buried it deep in his pocket.

A night on this tropical river, into which they had come for easier access to the Kennedy cottage, was a new and interesting experience for Johnny. Mangrove trees, growing far out over the river, all but touched the deck. A troop of monkeys, apparently planning to cross the river on swinging branches, came chattering along to burst into a sudden frenzy of fear and anger at sight of this intruder. Crocodiles floated lazily on the dark surface of the water. Their eyes shone like balls of fire when Johnny's flashlight was directed at them.

From the far distance came the singing of men and women, a native chant. A little later, paddles gleaming in the light, some of the singers floated past. Their large dugout was loaded with all manner of tropical fruits--bananas, pineapples, wild oranges and mangoes.

"What a life," Johnny murmured, as the natives drifted past. He thought of the conditions of thousands of persons in the great cities of America--then looked out again at that boatload of people. It would be grand, he thought, to live here forever. And yet, there were the spies, and debts to those Europeans.

"Debts," he sighed, "that haunt them till they die."

Doris came on deck. "You just _can't_ sleep on such a night!" she sighed. "It's too wonderful--the river, the moonlight, and the dark, mysterious jungle at night."

"And the spies," Johnny added. "Don't forget them!"

"The--the spies?" She stared at him.

He told her of his adventure with Mildred, and, of the mysterious night singers.

"They vanished," he ended. "Vanished into thin air. And they had a boat of some sort. We saw its mark in the sand."

"How thrilling! How sort of spooky!" she murmured.

"And there's the code of the green arrow," Johnny added. "We solved that--or rather Mildred did." He explained it to her.

"That sounds dangerous." She seemed a little startled. "But it--it doesn't affect us, does it?"

"No--oo--not directly," he responded. "But they are spies, all right! Their message shows that. You can't have counter-spies without first having spies. If they should chance to think that _we_ are the counter-spies, and that we're watching them from the steel ball, and--"

"The steel ball! How _could_ we?"

"Well," Johnny replied slowly, "perhaps we couldn't. That was just a notion. But we _could_ be counter-spies."

"But we're not!"

"That," he laughed, "is what they may not know."

"Oh, you and your spies!" she exclaimed. "You're always taking the joy out of life. Look at that moon!"

"I have been looking at it. Big as a barrel!"

"Gorgeous," she agreed. "Do you know?" she stepped over to the rail. "I've been thinking of that picture you suggested--the one painted beneath the sea. It would be wonderfully colorful--all those bright, tropical fish, the waving water-ferns, the coral, and all that. I'm going to try it, some time. Only--"

"Only what?"

"The sharks."

"They won't trouble you. I'll stay on deck and watch. If anything comes after you, I'll be right down. Is it a bargain?"

"I'll do it." She put out a hand and, solemnly, they "shook" on it.

Ten minutes later Johnny was alone with his thoughts, and the night. They were long, long thoughts. He was working out a theory about the messages of the Green Arrow, and the whisperings beneath the sea.

One question brought him up with a start. If these people were foreign spies--why did they speak in _English_? For a time, this was a poser. But then the answer came, and he threw back his head and laughed! Foreign spies, sent to America would be _required_ to speak English! If they were keeping in touch with some of their own people by short-wave--_of course_ they would speak English! Otherwise, anyone listening-in on their messages, would instantly suspect them.

That the messages of the green arrow also were in English, was not so easy to explain. "Perhaps talking and sending messages in English, has become force of habit with them," he told himself.

The night was long, too, and he was tired. He rejoiced when the first flush of dawn told him a new day was here.

Dave came on deck early. "We'll be getting out of here at eight," he said. "I guess you know that I'm taking Mildred down below, today. It'll be interesting to see how a girl reacts to all that strange environment. She seems a bit timid. But she asked for it. So--"

"There's someone _I'd_ like to take down," Johnny said, suddenly.

"Who?" Dave questioned.

"Old Samatan."

"In the name of goodness!" Dave exclaimed. "Why?"

"He acts very queer about that steel ball--looks as if he'd like to bite a chunk out of it, and I don't understand it."

Johnny hesitated. "Perhaps if someone took him down, it would clear up some mistaken notions in his queer old head. He seems to have a lot of influence with the other natives. If anything should happen--"

"Nothing will happen." Dave broke in. "This is the quietest place in the world."

"Do you think so?" Johnny asked, with a little smile.

Dave nodded, absently. "But if you'd like to take Samatan down," he added, "it's O.K. with me. Be a grand experience for the old fellow. He'd never get over telling about it."

"Soon?" asked Johnny.

"Any time you like," was the answer.

Thanking Dave, Johnny ambled off to his berth for a long and dreamless sleep.

CHAPTER VIII MONSTER OF THE DEEP

Morning came and, for Mildred--the ride in that steel ball.

Never in all her life had she been so thrilled, and so frightened. Curled up inside the sturdy metal sphere, she went down--down--down, into the mysterious depths of the ocean. The light from the quartz window seemed bright blue, yet she experienced trouble in distinguishing small objects within the ball.

The creatures outside the window were strange beyond belief. Here a great school of blue fish shot past. There a six-foot monster with waving tail sped on in swift pursuit of smaller fry. And a group of small, dark, crab-like creatures wriggled their way across the scene. A little farther from the window loomed a dark wall. She shuddered at sight of this. All too vividly she recalled Johnny's account of their harrowing experience on that other day.

At Johnny's first suggestion that she accompany Dave on this sub-sea journey, her impulse had been to say quite definitely--"No! I won't go!"

But she had not said it. She just must have Dave's help in finding their schooner. So--she continued to shudder as they went down--down--down.

Dave was at her side, saying never a word. Staring at the passing scene, now throwing on a powerful light, now switching it off again, he appeared to have forgotten she was there.

It was to be a very short trip, perhaps only half an hour. They were to make an attempt to capture some fantastic sort of creature. Mildred was thinking of this now, wondering in a vague sort of way, how the capture was to be made. Then suddenly, her thoughts were interrupted. Her heart skipped a beat as Dave exclaimed:

"Man! Oh, man!"

The steel ball was now close to the wall. For the moment, at a command from Dave, it had ceased dropping. Suddenly from a crevice in the wall there glided a form resembling a great golden serpent from a fairy tale.

"Zowie!" Dave chuckled, "he sure looks dangerous--but he's not. A golden-tailed serpent dragon," he explained. "They're quite rare.

"Now," he spoke into his microphone, "slowly downward."

Once more the rocky ledge appeared to glide upward.

"Should be there soon," Dave murmured. "Only hope the old boy is at home. He probably is. But we may miss him. It's hard to get the right location."

For Dave this brief expedition had one purpose--to capture the immense, sea-green octopus he had seen on a previous trip. As they continued to sink into the depths, his eyes remained fixed on that wall. Then of a sudden he exclaimed:

"There! There he is!"

Adjusting his microphone he said:

"Doris, we are here. Stop the cable drum."

The ball ceased to sink. For a full moment Mildred saw only a dark cavern in the wall. Then suddenly she was startled to discover two large eyes staring out at her.

A moment more and a long arm came wavering toward them.

"Doris," said Dave. His voice was steady. "Have them swing us out a bit. Ten feet may do." Then, seconds later, he said: "There. That's it."

He began working at something close beside him. As Mildred watched the dark cavern she saw an arm reach out, then another. For a time these appeared to wave aimlessly. Then they took direction. To her astonishment she saw that a steel rod had swung outward toward the octopus from the bottom of the ball. At the end of this arm were steel clamps, and in the clamps she saw a dead lobster. The terrifying tentacles of the octopus, appearing fully twenty feet long, were moving toward the lobster.

"The octopus feeds on shell fish--crabs and lobsters," Dave explained briefly.

"Now," he breathed, as one long arm encircled the steel clamps. "Now--I wonder what luck." Once again he worked at levers and small handscrews at his side. The clamp out there in the water half opened, then closed again. This was repeated twice. Then:

"Ah! Got him!" Dave's voice rose exultantly. Into the phone he whispered, "Doris. Out a little--and then up, at top speed!"

To her astonishment Mildred saw a great mass of twisting arms emerge from the cavern. One by one these arms wound themselves about the steel ball. One of these, a great scaly affair with little suckers on its underside, crossed the window. With a little cry of dismay she shrank back.

"He can't get to you," Dave laughed. "Even if he could, he'd be harmless enough, unless he drew you beneath the water and drowned you.

"You see," he added, "while the octopus was working to get that lobster, I opened the clamps. His arm slipped in, and I closed them. Now he's making himself comfortable for the ride. It will be a longer ride than you might suppose--all the way to the New York aquarium! And boy! Will he be something to look at! Largest ever captured, I'm sure--and sea-green at that. This being a naturalist is the berries, when things are right. All you have to do--

"Hello!" he exclaimed. "Here we are at the top, already. Now for some work."

Before making any attempt to get the big-eyed octopus into the ship's pool for live specimens, Dave assisted Mildred from the ball. When she climbed forth, she felt a cold chill course down her spine. Those great, scaly arms were not a foot from her head. But they did not move.

"Good boy, Dave!" the professor exclaimed half an hour later, as they watched the octopus surveying his prison tank in the _Sea Nymph's_ hold. "That is a real prize! A few finds like that and we will have more than paid our way.

"I like to think," he added, quietly, "that we are truly serving the millions of people whose only chance to see rare creatures of land or sea is in the zoos and aquariums."

"I am sure it _is_ a great service," Mildred exclaimed. "But professor! What spooky waters those are down there!"

"Yes, they are spooky," the professor agreed. "But today, I take it, they were not whispering?"

"No," the girl agreed. "The whisperer seems to have vanished."

"These little undersea journeys always make me hungry," said Dave. "Come on Mildred--let's have a cup of tea."

Seated under a colored umbrella on deck, they sipped their tea in silence. Mildred was thinking--"I wonder if this is the time to ask him?"

It was Dave who at last broke the silence.

"Well, Mildred," he said, "you behaved very well for the first time down. I was wondering--"

"If a girl could take it," she smiled. "Down here we just have to--all the time."

"How so?" he asked in surprise. "In what way?"

"Well, only a few days ago grandfather lost his motorboat. It's somewhere at the bottom of the sea, but not far down. I wasn't on board when it sank. And now," she hesitated, "now fresh dangers appear to threaten us, and we have no boat either for trading or--or for escape!"

"Escape? Escape from what?" Dave ejaculated.

"Well, we might have to escape, you see." Mildred leaned forward eagerly. Her eyes shone. "Grandfather always has opposed those men--spies, really--who are trying to get all the islanders under their control. So they hate him. Just recently--"

She went on to tell of the code message flashed by the green arrow and of other strange and unexplained happenings. "Of course," she added, "nothing has been _done_ yet. But you never can tell."

"And you want me to help you find that motorboat of yours, with my steel ball? Am I a good guesser?"

"You certainly are," the girl replied, frankly.

"And you didn't really want to go down in the steel ball--you were terribly frightened by the thought? But you believed it might help, so--"

"So I went," she breathed. "You don't mind, do you?"

"Mind?" he exploded. "I think you are a grand, brave, little girl. If you were my sister,"--he paused to grin good naturedly.

Smiling back at him, Mildred felt sure she would be aided in her search for her grandfather's motorboat. The thought made her very happy.

CHAPTER IX DAVE'S ELECTRIC GUN

Once again it was night.

Johnny walked slowly back and forth along the narrow deck. There was about him on this night a sense of uneasiness, as if some unusual thing was about to happen, or possibly a whole succession of things, which might change the whole course of his life.... That very evening he had heard old Samatan making a speech to the native crew--a fiery sort of speech, with the men uttering grunts of approval every now and then.

"I'll take him down in the steel ball tomorrow, if I get the chance," Johnny assured himself. "That should cool him off!"

Samatan, however, was not the only cause of his uneasiness. There was the sign of the green arrow, those singers, and the boat mark on the beach--and Mr. Kennedy's constant talk of spies. All these, he felt, were part of a strange pattern of events.

"The whole thing may blow up any time," he told himself. "And then what--" His thoughts were interrupted suddenly. He sprang forward. He could swear he had seen something move near the steel ball.

"No one here now," he murmured, circling the ball, slowly. "Imagined it, I guess. My nerves are jumpy tonight."

A whole succession of small, dark clouds, high in the heavens, had been passing before the moon. One moment the deck was white with moonlight; the next, it was dark as the deep sea.

Johnny laughed softly, and found it helped steady him. Taking another turn 'round the steel ball, he walked past the open top of the tank in which the giant, sea-green octopus was kept. As he came alongside, there was a sudden splash--as if the creature had thrown out a long arm and allowed it to drop. It gave him a real start. Suppose the monster reached out for him and really made connections. Suppose--

There was that darting shadow again. Or was it? Just then a big cloud hid the moon.

"It's nothing," he assured himself. "Can't be. Crew's all asleep. No chance of anyone coming on board without being seen. Guess I'll have to take a good, long, drink of cold water."

Going to the stern he obtained his thermos bottle, uncorked it and drank.

Then he dropped into a steamer chair to await the reappearance of the moon from behind that big, black cloud.

The cloud still obscured it when, swift as a shot, he leapt straight into the air, as from the octopus tank came a shrill, hair-raising scream of terror.

"Great Jehosophat!" he exclaimed as he sprinted down the deck.

One flash of his electric torch showed a hand waving wildly above the surface of the water. An instant later a head bobbed up. Eyes wild, nostrils dilated, the mouth opened in another unearthly scream as the victim vanished beneath the water, now thoroughly roiled by the octopus' savage threshing.

Long slimy arms appeared--here, there--seemingly everywhere. Then again, a man's head broke the surface.

But now Johnny was on the steel ladder, reaching for the hand that had followed the head above water. Seizing it, and wrapping his left arm about a rung of the ladder, he pulled with all his might. That he was taking his life in his hands, he well knew. Those scaly arms seemed to be feeling for _him_. If they reached him--

All the while, Johnny was thinking, "Who is this person and how did he get on board?"

Thanks to Johnny's good right arm, the man's head remained above the surface. He was a swarthy individual, with short-cropped, black hair. Spitting out a quantity of water, he whispered hoarsely:

"Don't let him! Don't let him pull me back under!"

There came a sudden tug that all but broke Johnny's grip on the man's hand. At the same time, waving above the disturbed surface of the tank, a long, slimy arm seemed to feel for the boy on the ladder.

Then, to Johnny's vast relief, came Dave's voice, calling:

"Johnny! Johnny Thompson! Where are you?"

"Here! Here in the tank! Help--and _hurry_!" Johnny shouted, desperately.

There came the sound of running feet along the deck. At that very instant, a scaly tentacle found Johnny's wrist and wrapped itself about the two hands, binding them together as with a band of steel.

"Wha--what's happened?" Dave threw a flash of light on the fantastic scene. His quick eye took it all in at a glance. "Hang on, Johnny! I--I'll be back in a jiffy!" Then he was gone.

The tremendous power of that steady pull from the tank, promised to wrench Johnny's arm from its socket. The stranger in the pool uttered a low groan. Johnny's mind went into a tailspin, but he hung on desperately. How would this end? Would Dave _never_ arrive?

"Now!" came from above, and Dave was back. In one hand he held an automatic, and in the other, what appeared to be an iron rod.

"Get ready for an electric shock," he said, quietly. "I think this will fix him."

He thrust out the rod until it touched one arm of the octopus. Next instant, Johnny felt a powerful electric shock that brought his muscles up with a jerk. Again, and yet again came the shock. Johnny could hear the stranger's teeth chatter. Then he saw the fellow's other hand. It was free. At the same time the scaly thing about his wrist began to relax.

Giving a powerful pull, he lifted the stranger half out of the water. Twenty seconds later they both were free, and tumbled, panting, on the deck.

For a full minute Johnny lay motionless. When at last he sat up he said to Dave:

"Hang onto that gun. You may need it."

Turning to the swarthy stranger he demanded:

"What were you doing on this boat?"

"I was just a-passin' by, and took a notion to climb aboard," the stranger muttered.

"You are lying," said Johnny. "You were spying into things! Why?"

"I wasn't spying! I don't know what you're talking about," said the man.

"I don't think he's a spy," said Dave. "He's just some native."

"Native, my eye!" snapped Johnny. He had noted the outline of a long knife, showing through the fellow's wet garments.

By this time the native crew was swarming up from below, and Doris and the professor were standing in the shadows.

"Let the fellow go," Dave whispered to Johnny. "He's just some native who happened by in a dugout, saw our boat and thought he'd have a look. He might have meant to steal something, but you can't prove that. We don't want to get these natives excited. They might leave us in a body. Then where would we be?"

"Oh--all right," Johnny agreed, reluctantly. To the man he said: "Come with me."

The man's boat was tied to a belaying pin up forward. As they walked in that direction, Johnny and the intruder were out of sight of the others, for a moment.

"I'll just take this to remember you by," said Johnny, dragging the man's knife from its sheath. "If you're a native--you should carry a machete."

The man favored him with a mocking smile, then bolted over the rail into his small boat and was gone.

"Well, that's that!" said Johnny, as he rejoined the others. "Here's hoping he doesn't come back."

"Johnny," said Dave, "I wonder if you weren't making a whole lot out of a very little."

"Perhaps I was," Johnny answered quietly. He saw no point in arguing.

A moment later he said: "Dave--what was that thing you shocked the octopus with?"

"That was an electric gun," Dave laughed. "We use it while we're exploring the sea-bottom on foot. If some big fish, like a shark, gets too curious--we touch him and pull the trigger. Believe me, they beat it!

"It's lucky I had it," he added. "Otherwise I'm afraid I should have been obliged to kill our prize, and that would have been a great loss. By the way, Johnny, how did that fellow get into the tank?"

"Tumbled in, I suppose. Probably thought he was going down into the hold to prowl around."

"I wonder why?" said Dave.

But Johnny didn't see fit to discuss the matter further.

After the others had retired again, Johnny took the stranger's knife to the light and examined it closely. Never had he seen such perfect workmanship. The blade was of hand-forged steel, with a handle of old ivory. Two foreign words were stamped on the blade. Johnny could not read them, but he knew very well this was no native's knife.

"A spy, beyond a doubt," he muttered. "Wonder how many there will be tomorrow night. Dave must let me have a gun!"

Just then the moon came out from behind a cloud, flooding the deck with white light. What a difference that made. All the mystery of the night seemed to fade.

Johnny shrugged his shoulders and continued to pace the deck.

CHAPTER X LITTLE BIG-HEADS

Next day Johnny took Samatan for a ride in the steel ball. He had supposed it would be difficult, if not impossible, to induce the dignified old native to accompany him, but he was due for a surprise.

"Samatan," he said pleasantly, "you know we have been making trips far beneath the surface of the sea in that steel ball."

"Yes!" Suddenly Samatan was alert.

"Dave and I--we--well we thought you might like to go down."

"In the big ball?" The native's eyes shone, eagerly.

"Yes, that's right." Johnny answered.

"Today?" asked Samatan.

"If you wish."

"In one hour," said Samatan.

An hour later, Samatan took his place beside Johnny in the steel ball, watched the massive, steel cap being screwed into place, felt the bump of the ball on the deck, then sensed their drop into the sea. All this--in stoical silence.

Down they went, a hundred feet--two hundred--five hundred--a thousand. By the small light at his side, Johnny watched the native's face. The expression never changed.

"He seems to be expecting something interesting and exciting," the boy told himself. "Wonder what it could be. If he's afraid, he sure doesn't show it."

As they sank lower and lower, the darkness increased. At last, as Johnny threw off the electric light and all about them was inky black, from the native's lips came a hiss of surprise. That was all.

When Johnny threw on a powerful light, the look of expectation on Samatan's face returned.

"Strange sort of person," the boy thought. "What can he be expecting to see?"

They were now standing still. The professor on deck, had decided their descent had gone far enough.

As Johnny sat staring into the inky blackness before them, he gave a sudden start, then snatched his camera. There, plainly in view, was one of the strangest monsters he ever had seen.

Scarcely had he adjusted his camera for a picture, than a second creature appeared.

"Must be a school of them." His hand trembled a little.

Just as the camera clicked there began the most amazing and terrifying experience of Johnny's eventful life. As though pushed by a giant hand, as a child pushes a playmate in a rope swing, the steel ball moved rapidly outward and upward--although Johnny had given no signal!

Outward and upward--one hundred--two hundred--three hundred feet. Who could say how far? What mysterious power motivated this wild ride, and where would it end? Would the cable snap?

Johnny made no effort to conceal the horror reflected in his face by this thought. Sealed in a steel ball, resting on the bottom of the sea, half a mile or more below surface. What chance? The boy's lips moved, but no sound came. Then, by sheer will power, he adopted a calmer mood and waited the turn of events.

Samatan neither moved nor spoke. Strange Samatan! Did he think this was part of the show? And what had he been waiting so patiently to see?

There was even greater consternation on board the _Sea Nymph_.

Dave had gone ashore for a bit of dry-land exploring but, with Doris at his side, the professor stood watching the pumps that sent air to the occupants of the steel ball. His gaze, reflecting serious concern, was focused intently on the gauge registering strain on the steel ball's cables.

"Doris!" he exclaimed excitedly. "Look, Doris! _Look! The strain has doubled!_ The cable is perilously near the breaking point!"

"Poor Johnny!" Doris cried, distractedly. "Down there with old Samatan! If the cable breaks--"

"If the cable breaks--no power on earth can save them!" The professor's voice dropped. "The bottom must be a full mile down and I doubt whether the ball could withstand the terrific pressure. Nor is there any way we could bring it to the surface!"

"What can be done?" Doris was wringing her hands.

"Pray!" was the professor's simple reply. "Strange things are accomplished by prayer, and faith."

Doris _did_ pray. Then they waited in silence. Ten seconds ticked their way into eternity. Twenty--thirty--sixty. The arrow of the gauge moved nearer the "maximum strain" point at the top of the dial--and stood still. Then, for a brief second, it moved forward again.

"The cable! It can never stand the torsion!" the professor groaned.

Just as all seemed lost, the arrow quivered--and began, slowly, to move the other way.

"Thank God!" exclaimed the professor, fervently. "It--it's going down, Doris, child."

Staring at the dial, Doris opened her lips in silent thanksgiving. She could only stand and stare.

What had happened?

That was a question that remained unanswered for weeks. Some tremendous power behind the steel ball had pushed it away and up, until its certain doom seemed inevitable.

Then, with a sudden, rolling lurch, the ball had been freed and at once began sinking to its original position. Fortunately, the resistance of the water was so great, there was no danger that the stopping of the descent would snap the cable.

As they reached bottom position, Johnny grabbed Samatan's hand and gripped it, impulsively.

Then it was that the native said a strange thing:

"You go bottom now?" he asked, hopefully.

"No," said Johnny, happily. "But we are _safe_, man! I'm signalling them to draw us up!"

"No go bottom?" There was a suggestion of disappointment in Samatan's voice.

Suddenly Johnny thought he understood. Samatan had expected to see bottom. That was what he had wanted, and it explained his strange eagerness to go down. But _why_? What did he expect to see there?

Johnny, however, was far too eagerly awaiting the first, faint gleam of light as they rose, to think much more about Samatan's behavior.

The strange "dawn beneath the sea" came to him once again. Such a glorious dawn! He was to live on! What a privilege it became, suddenly, just to live! The ball rose free of the water, to swing about and bump gently down to the deck. A few moments later, the professor and Doris were gripping his hands and demanding to know what had happened.

"What in the world went wrong?" they asked, in chorus.

"We ran into a school of monsters." Johnny was now able to laugh at his predicament. "They must have taken us for a ride, I guess!"

"What kind of monsters?" The professor was so serious his voice trembled.

"You won't believe me if I tell you," the boy replied, soberly, "but here goes. They had heads twice as large as their bodies! And those heads! If only their mouths had been a little larger, they might have swallowed our steel ball at one gulp!"

"Did they have a small lower jaw and a large upper one? Were their eyes set well back on the side of their heads? Did their tails wave like those of some tropical fish?" The professor was growing excited.

"Yes, yes, and yes," Johnny laughed again. "But say--I tried to take pictures of them! Wonder if they could have been good! Wait till I get my camera." He made a dive into the steel ball to reappear at once with the camera.

"But Johnny!" Doris insisted, "you haven't told us what really happened?"

"I don't know, and that's a fact!" replied Johnny, quietly, soberly. "I was just taking pictures of those beasts when--"

"They're known as little big-heads," the professor broke in, "and they are rare, indeed! You are the first person ever to see them alive. Two specimens have been found washed up on coral beaches, dead. You are a truly great explorer, Johnny! You may now take a bow."

"Aw, say!" Johnny fairly blushed.

"Anyway," he insisted, "one of them must have become tangled in our cable, and in his wild efforts to free himself, took us for an underseas joyride!"

"That doesn't seem possible," mused the professor, slowly. "I should like to know what really happened."

"So should I!" Johnny agreed. "All I have to say is--I'd like them to stay clear of our cable, in the future! Please look at my hair! Do you think it will turn white?"

"In thirty or forty years," Doris laughed. "But Johnny--we're dying to see those pictures."

"Yes, yes!--by all means!" the professor agreed. "Let us see them at once." So they crowded into Johnny's small darkroom to watch the enthralling "coming out" of one more set of plates.

* * * * * * * *

"Little big-heads," the professor whispered solemnly, as the pictures began to appear. "Johnny, you are a wonder! Once again we have registered a real triumph!"

"I'm glad of that," Johnny said, sincerely. "I like being a success. But even better--I enjoy living!

"I'm sure I'll not be able to sleep in the dark for months to come," he said, more lightly. "I'll be imagining I'm still in that steel ball, swinging wide in utter darkness!"

"Johnny," Doris whispered some time later, "What _really_ took you for that ride?"

"I could only guess--and it would be a wild guess, at that!" There was a suggestion of mystery in his voice. "I'm sure of one thing, though. It wasn't any little big-head!"

CHAPTER XI TIGERS OF THE SEA

Doris, standing on the ocean's floor forty feet down, started back in sudden terror, and her foot struck a rock. She all but fell over. On the beach she would have taken a terrible tumble.

"It was just a shadow," she told herself. "Only a shadow moving beyond that great rock. A blue shadow. Grandfather said I'd be in no danger, and he should know."

Involuntarily she put a hand over her wildly beating heart, then smiled at her action and at once felt better.

"I must finish," she told herself, stoutly, as she resumed her task.

She was painting a picture. The circumstances under which she worked were strange, almost beyond belief. When Johnny had suggested an underseas picture, she had been truly thrilled. But she had shuddered and said, "No!--I'd never dare do that!"

But--given one glimpse of the setting for such a picture, she had become greatly excited. "Such colors! Such contrasts! Yes--I surely must paint it!" she had exclaimed.

The task now was well begun. She was wearing tennis shoes and standing on sand. Before her a great anchor, red with rust, leaned against a huge boulder. Beside the anchor was a copper-bound chest. One might easily have imagined that this chest contained Spanish treasure--gold, diamonds, rubies. But it was empty, as Doris already had discovered.

The gray rock that supported the anchor was festooned with vegetation of rare hues--red, orange, pink, yellow, and deep dark blue, mingled in profusion. In and out among these plants darted small creatures which might almost have been birds. The girl was wearing a great brass helmet which hid her face. She was looking through glass, at a world unbelievably strange and beautiful.

Above her, its shadow looming darkly, lay the _Sea Nymph_. Descending from the boat was a long tube that supplied her with air. A constant trickle of bubbles escaped from beneath her helmet. Her easel was weighted down, and her canvas specially treated to resist water. Her brushes and colors were the same she had used on the sunny, tropical shores.

But the scene! How she thrilled to it! And she was painting it as truly and exactly as she could. Perhaps thousands who never had been beneath the surface of the water would look at this picture and wonder at its coloring.

Thrilled at the thought, she painted more industriously than ever, forgetting entirely the blue shadow. She had searched long for a spot that would make the most interesting picture. She had wandered, fascinated, until she had chanced upon this anchor and strong box, lost so long before.

It was indeed wonderful. With a background of ivory and pink coral, purple plumes of seaweed, fringes of lace-like anemone, in a framework of water-washed rocks--it made a scene not soon to be forgotten.

So here she was, painting rapidly--though far back in her mind was the memory of that blue shadow behind the rock....

The scene was forever changing. A cloud passing over the sun, dimmed the colors. Then a large school of small fish, darting forward at a furious rate, completely shut off her view.

But now! "Ah, now!" she thought, joyously.

A dozen tropical fish, the brightest and best she ever had seen, came to play about the ancient chest and "pose" for their pictures. With quick, deft touches she painted them in--two, staring large-eyed at the anchor--three, peering into the ancient chest, and three just "resting".

But what was this?

Like a flock of birds that have caught sight of a circling hawk, the tropical fish darted swiftly away. Had they caught a glimpse of a dangerous foe, gliding from behind the rock? The girl thought so, and shuddered. She even fancied she had caught its color again--dark blue. But of this she could not be sure. Down here all was so strange.

"A villain," she murmured to herself with a low laugh. "The final touch to a gorgeous setting."

To quiet her shaky nerves she gave herself more intensively to completion of her task.

"There is no danger," she assured herself again. "Grandfather says there is absolutely none--and he has spent days on end on the ocean's floor."

She recalled his very words: "Oh, yes, there are sharks in these waters--but they won't harm you. If they should get curious and come too close--poke them with your stick! I've done that more than once."

Scarcely had she gone over these reassuring words when something startled her, anew. A dark shadow appeared suddenly at her right. She took one look, then laughed. "It's only a fish," she thought.

Brushing away two tiny fish that had managed to get themselves stuck to her canvas, she began giving her work its final touches.

For ten full minutes she worked feverishly. "My time is almost up," she was thinking. "They will be giving me the signal. Then up I'll go. But I do so want--"

Her thoughts were suddenly arrested. What was that? She had felt the motion of water against her body. "As if something passed--fast!" she thought with a little shudder. Turning slowly about, she peered through the window of her brass helmet.

"Nothing," she whispered. "Nothing but three long, gray fish, over there. But what of that? I--I'll give my signal rope a pull," she told herself. "Just a minute more and I'll do it."

The minute stretched to two, three, four. And then it happened. One of the long, gray fish flashed like a streak of doom, straight for the hand that held the paint brush. Missing by inches, it collided with the easel, knocked it to the sea floor and shot away in sudden flight.

The fish could not have been more frightened than the girl. Suddenly she recalled wild tales told by the natives about the vicious barracuda--"Tiger of the Sea." ... A woman had dabbled a finger in the water--and one of these fish snapped it off.... Swimmers had lost toes.... She felt paralyzed with fear.

Then, like an act in some strange drama, a pair of dangling legs appeared between her and the gray terrors. The legs were followed swiftly by a body, a brass helmeted head and two hands, holding a sharp-pointed spear.

The spear shot out!

The gray terrors, like arrows from a bow, flashed out of sight. It seemed to Doris that no creatures ever had moved so rapidly beneath the surface of the sea.

She watched the "apparition" in a helmet--which she knew to be Johnny--take up her easel and set it in position. She noted, vaguely, that the picture had landed right side up and was not harmed. Then Johnny turned and held out his hand.

She expected to be taken straight up to the ship's deck. Instead, he led her a distance of a hundred feet along the bottom. Then they came to an abrupt halt, and Johnny pointed straight down.

She looked--and involuntarily stepped back. They were standing on the very brink of a yawning, watery precipice. Far down as one could see was only blue-black depth. It was an awe-inspiring sight.

As if to add to her amazement, she saw--perhaps a hundred feet down--some large, dark hulk. It was dim and indistinct as a shadow, yet very real, as it moved slowly along the cliff, to disappear in the blue-black of the apparently bottomless ocean.

This had not been part of the planned show, she knew at once from her guide's actions. He moved his arm, pointing excitedly.

A moment longer they stood there, looking down. Then came the signal to come up. The picture and paints were attached to the easel, and a cord drew them up. All Doris had to do was to give a little spring, and up, up, she rose, to the glorious sunshine of a tropical day.

A quarter of an hour later, she and Johnny were seated on the deck, laughing at one another and scarcely knowing why.

Dave and the professor had gone ashore to study tropical bird life, so after the evening meal, Johnny and Doris sat on deck watching the play of phosphorescent creatures beneath the surface of the sea.

"This," said Johnny, "is my day off. Tonight I sleep. Tomorrow old Samatan and I are going for a sail in a large dugout, to visit some coral reefs."

Doris smoothed back her thick, golden hair, fixed her bright blue eyes on him, and said: "Why?"

"We need him for a friend," Johnny replied, quietly. "If _he_ is with us--all the native crew will be, too. He's a leader."

"You talk," said Doris, "as if there were to be war!"

"Who knows?" Johnny did not laugh. "Perhaps there will be, but not just yet. There are spies with us now!"

"How do you know?" She leaned forward in her chair.

"That man I caught on board the other night, was a spy. Look!" He held up the exquisitely wrought knife. "Do you think a native would have such a gem of a knife? Not a chance!

"Then--there's the green arrow to prove he's a spy!" Johnny went on. "One of the messages I spelled out by using their code read: '_Board them. Discover all you can._'"

"But why?" said Doris. "We're not secret agents."

"That's what _they don't know_! We are Americans--and they don't want us around."

"Know what?" Johnny continued, "I believe that big thing that glides through the water--the thing we saw today--is a submarine!"

"It can't be!"

"Why not?"

"Well, if it is--it must be an American submarine!"

Johnny looked at her for a moment in silence.

"It's not an American submarine," he said, after a time. "I've seen them, and this one's the wrong shape. It's some spy submarine, looking over the bottom of the sea and getting information for the next war. I shouldn't be surprised if a large part of that war were fought right in this Caribbean Sea!

"What's more,"--he rose to his feet--"I'll bet a dollar that the thing that took Samatan and me for a ride in the steel ball, _was that same submarine_!"

"Trouble with you," Doris laughed merrily, "is too much imagination."

"You just wait and see," Johnny replied with a smile.

The sound of oars at this moment, announced the return of Dave and the professor from their day's explorations.

CHAPTER XII JOHNNY'S DAY OFF

Next morning Johnny and old Samatan sailed away toward the smiling face of the rising sun.

"This is a grand dugout you've got!" Johnny enthused.

Smiling, Samatan pulled a line, giving the boat full sail. She tilted sharply. Boy and man settled back against the pull of the sail and sped along before the wind.

Johnny's eyes took in the whole of the trim little craft, and he smiled, contentedly.

It was indeed a great little dugout. Not so small, either. Fully twenty feet long and six feet wide, it had been hewn from a solid mahogany log. The boy tried to estimate the number of days of hard, careful work that would have required, but gave it up.

The inside surface was polished to the last degree, and the seats were braided, cocoanut fibre. On the prow, carved in the most perfect manner, was the wooden image of a seagull.

All unknown to Johnny, Samatan was keeping an eye on him. His keen old mind read the boy's thought like a book. One lover of a sailboat recognizes another, and since his tenth birthday, Johnny had been an ardent sailboat enthusiast. At that age he had rigged up a square sail for a rowboat and had known many happy hours on the water. The fact that he had once capsized and barely escaped drowning, had not in the least dampened his ardor.

"We go coral reef. Catchem turtles for stew," Samatan said at last.

"How do you catch them?" Johnny asked.

"Samatan show you."

After that there was silence.

It became evident that Samatan was an expert with a sail. The breeze picked up and the sea became choppy, but the smiling old man, eyes squinting, lay back at ease. Pulling first at one rope, then another, he held the small craft on her course.

Johnny laughed right out loud when at last the old man took off his soft, loose shoes, gripped the ropes with his toes and began steering with his feet.

Two delightful hours passed. Then the dugout slid up on a sandy shore.

When the boat had been pulled up, Samatan's eyes scanned the sandy beach. Suddenly he went racing away and, with the silence and speed of a great cat, stole up on an unsuspecting turtle, basking in the sand. A quick leap--and the turtle lay on its back, a prisoner.

"Food," said the old man. "Much food from the sea. But," he added quietly, "we take only what we need."

When all the turtles needed had been stowed away in the boat, they went for a walk on the beach. They made a strange picture, this bright-faced American boy and the old, brown native whose face was wrinkled by many tropical suns.

Seldom had Johnny spent a more interesting or exciting morning. They hung a heavy cord over a rocky ledge to snare a sea-crab, turned over a Hawk's-bill turtle, whose shell was worth eight dollars a pound, and chased a monkey up a cocoanut tree.

They had wandered for two hours and were far from the boat when, for no apparent reason, Samatan uttered a low exclamation. Then he faced squarely toward the ridge, which at this place rose some twenty feet above the beach.

"Huh!" he grunted. "We see!"

He dashed away at surprising speed, up the hill. Tripping over vines and blundering into a bramble bush, Johnny followed.

When at last he caught up with the agile old man, Samatan was standing motionless, looking off at the sea. For a full minute, lips parted, eyes staring, they stood there in silence.

For--stealing up on them like an enemy in the night, a terrific storm was racing in from the sea. It took but one word from Samatan's lips to complete the terror of the prospect.

"Hurricane!" he said, gutterally.

"We must run for the boat!" Johnny sprang down from the rock.

"Not go now. Too late!" Samatan did not move. Instead, he stood looking along the ridge, first this way, then that.

"The _Sea Nymph_!" Johnny broke out again. "She will be lost!"

"Not get lost," Samatan said, slowly. "Good crew. Harbor not far." Once again his eyes swept the ridge.

"Come," he said at last. "This way. We go fast." Even as he spoke, a gust of wind sweeping in from the sea, all but threw the boy off his rocky perch.

For ten minutes or more the two of them fought their way along the ridge. At last the native paused. "Here," he said, "is most high. Trees. Must climb these--quick! Waves go all over coral reef!"

"Al--all right." The rising gale blew Johnny's words down his throat. Seizing the low branches of a large tree, he prepared to climb.

"No! That bad tree! No good!" said Samatan. "This one."

Into Johnny's mind at that moment came the words of the professor: "When I am in a strange land I do what a native will do--go where he goes. If he says 'No go'--I stay."

So, without further questioning, the boy began to climb Samatan's tree.

The tree was short and sturdy. Soon they were perched like crows on two limbs close together. And in silence they watched the onrushing storm. The sky was black. It was like night. Scarcely could the boy see his companion. Trembling with excitement, he decided to force his thoughts from the impending hurricane.

"Samatan," he said, "there was something about our steel ball you did not like."

"Yes," came the instant reply. "Professor--he is good man. Very good. But one thing must not do. He must not!"

"He is going to tell me," Johnny thought, with quickening pulse.

But at that moment there came such a roar as would drown the strongest voice, and onto the beach came the rush of a great sea. Something like a tidal wave had struck the narrow reef.

"I must hang on," the boy thought. The next instant he was engulfed in stinging salt water. The sea had swept over the land.

Though Johnny felt that he was being swallowed by the sea, it was in reality only the froth and foam of the monster wave that reached him. One instant he was gasping for breath, the next, he was looking down on a madly whirling world.

The thought that struck him first, with the force of a blow, was--"the tree I meant to climb is gone! Swept away by the sea!"

It was true. The tree, rotten at the roots, had vanished. Samatan had saved his life, and a new sense of respect for the aged native swept over Johnny. With it came the conviction that whatever it was the old native wanted from the professor, it must be right for him to have it. And something seemed to assure Johnny that he would hear the story without asking.

But at that moment, to talk at all was impossible. The shrieking of the wind, the cracking of branches, the roar of thunder and the mad tumult of the sea, were completely deafening. Johnny wondered how long it would last? Would greater waves come? Would he and Samatan at last be swept into the sea? To all these questions he found no answer.

In an effort to forget the terror of the situation he made himself think once more of the great steel ball and his adventures beneath the sea....

In the meantime his companions on the _Sea Nymph_ were witnessing a feat such as even the gray-haired captain never had seen equaled. Watching the storm, yet fearing for the safety of Johnny and Samatan and hoping against hope that they might return, they on the yacht had delayed lifting anchor.

When at last they headed toward the narrow entrance of a natural harbor, the wind tore their sails to ribbons, while waves, mountain-high, swept them toward a rocky wall.

In despair, the captain trusted the fate of his ship to the native crew. Nor did he trust in vain. With a few yards of sail at their command the natives, in the midst of dashing spray, clung to spar and masthead, turning the graceful craft this way and that. Then--at precisely the right instant--they seemed to lift her from the sea and send her shooting through a channel so narrow it seemed the paint would be scraped from her two sides at once. They sent her gliding smoothly to safety, in a harbor as calm as a millpond.

"Bravo!" shouted the captain.

"Glorious!" the professor cried. "Never saw such sailing! Those men deserve all praise!"

Six long hours the storm roared on, and for six endless hours Johnny clung to his tree. Though the sea, like some menacing monster, appeared to thrust out long, white arms to grasp him, he remained safely with Samatan, in the tree top. At last, sweeping high overhead, the storm-clouds raced away--to leave a kindly, golden moon looking down on the boy and the old man.

"Come," said Samatan, climbing gingerly down from his perch. "We go back."

"Back to what?" Johnny's lips framed the words he dared not speak.

Their trail back over the moonlit beach was strange beyond belief. They climbed over a huge old palm tree, lying on the ground, stumbled on a giant, loggerhead turtle, killed in the storm, and slipped on jellyfish left high on the ridge.

As they rounded a bend in the beach, a large object loomed before them, white and ghostly in the night.

"Boat," said Samatan.

"Lifeboat," the boy amended as they came closer.

Examining it closely he read the words: "S. S. Vulture". Bashed in at the prow, the boat lay empty, upside down. What was its story? Had the Vulture been wrecked? Had part of her crew put to sea in this boat, only to perish?

With a shudder, Johnny pushed on behind his tireless guide.

"Our boat must be gone," he ventured at last.

Samatan made no reply.

More fallen palms, tangled sea moss, jellyfish, a dead crocodile, a mile of sand, and then--Johnny rubbed his eyes. He opened them to look again.

"Our boat!" he exclaimed.

"Yes," Samatan said.

It was true. The boat was safe. Piled with seaweed and half-buried in sand, it remained where they had left it.

A brief examination redoubled the boy's admiration for the aged native. The dugout had been chained to a stout, palm stump. Even the sail was lashed beneath the seat. Samatan had taken all these precautions before there was any sign of a storm. Wise old Samatan!

In awed silence Johnny helped to clear the sand and seaweed away.

"Now we go," said Samatan, preparing to launch the boat.

If Johnny had admired Samatan's sailing before, his admiration was doubled now. Up--up--up they glided, until they seemed ready to touch the stars, then down--down, far into the trough of a wave.

"Samatan." Johnny spoke without thinking. "Why do you hate our steel ball?"

"Hate? Ball?" Samatan struggled for the right word. "Good man, professor. But must not steal natives' gold!"

"Gold?" Johnny ejaculated. "I don't understand."

The tale the old man told, then, out there on the racing sea, was fantastic indeed. Yet Johnny doubted never a word of it....

The islands now belonging to Samatan's native people once had been a French colony. The French had made slaves of the natives, and had brought in many more slaves. Then the slaves revolted and drove all the Frenchmen from the islands.

"After that--_our_ land!" Samatan declared proudly. "Long time republic. Long time everybody happy. Then," his voice dropped, "how you say it--came bad man. Very hard man. Very cruel. Make people work too hard. Want gold. All gold. By and by want kill that man, my people.

"This bad man see strange men come--many men." Samatan continued. "They put gold in chest--much gold--and dump in sea.

"Now," Samatan sighed, "bad man dead. Gold lost. Never find that gold, my people. Belong my people--that gold! Find gold--my people pay debts. Very happy. But now," he frowned, "Professor, he hunt gold with steel ball. Wanna keep that gold, you think, that professor?"

"Oh, no! No!" Johnny laughed. "The professor is not looking for treasure! Only strange fishes, all sorts of odd creatures that live beneath the sea."

"Not wanna find gold?" The old man was plainly puzzled.

"Oh, sure--I s'pose he'd _like_ to find it," Johnny laughed. "And--we'll really try to--now that we know about it. But if we _do_ find it, you may be sure it will all be for your people--to the last doubloon!"

"Good boy, Johnny." The old man smiled broadly. "Good man, Professor. All good. Everybody!"

"I see a light," said Johnny. "That must be Kennedy's place."

"Right, Kennedy." said Samatan. "By and by we come that place."

"That," said Johnny, "will be swell!" Then his brow wrinkled. Where, he wondered, was the _Sea Nymph_? Did it make harbor safely? He sighed as he reflected that soon he would know the answer--for better or worse!

CHAPTER XIII THE GREEN ARROW TRAIL

While Johnny was going through his wild adventure, Doris and Dave were not without their own exciting moments. Of course while the storm lasted, the professor's party remained inside the _Sea Nymph's_ cabin. As soon as it abated they immediately went ashore.

Troubled as they were at thought of Johnny's possible fate, there was for the moment nothing they could do. The seas were still running high. Dave and the professor went for a tramp in the jungle, while Doris followed the trail to the Kennedy home.

Mildred appeared greatly worried when told of the journey Johnny and Samatan had undertaken.

"But why did Johnny go?" she asked in surprise.

"Oh," replied Doris, "he had a notion that Samatan was angry about something. He said we might need the help of Samatan and his men."

"How?" Mildred asked.

"That's it--how?" Doris laughed uneasily. "He thinks there are many European spies around here!"

"Well--there are!" Mildred nodded her head vigorously.

"You, too?" exclaimed Doris. "But anyhow, Johnny thinks the spies believe _we_ are looking for _them_--and that they'd do something terrible to us."

"I shouldn't wonder," said Mildred.

"How comforting you are!" Doris smiled ruefully. "Just when I want to feel quiet in my mind! You aren't helping a bit!"

"Well," said Mildred, "how can I? There were those men singing in some foreign tongue. They just vanished! And there's that mysterious, blinking green arrow."

"Two of them," Doris corrected. "One on land and one on sea--like Paul Revere!" she chuckled mischievously.

"But of course," she added more seriously, "there was the man who came on board our boat, sneaking around, and went into a huddle with the octopus! That would have been funny had it not been so terrible. He had a knife that Johnny says no native would carry. But I don't see--"

"There are a lot of things we don't see!" Mildred broke in. "For instance--who was that whisperer who was always breaking in when Dave and Johnny in the steel ball were being dragged against the rocks?"

"He might have been a thousand miles away. Radio's like that," Doris said, doubtfully.

"Yes-and he might not!" Mildred exclaimed. "He appeared to know too much for that."

"One more thing," Doris laughed. "Johnny thinks there is a submarine--a foreign one--in these waters!--He thinks we saw it, and that _it_ was the thing that dragged the steel ball, that day!"

"I shouldn't wonder a bit," said Mildred.

"Oh, bother your 'shouldn't wonder'!" exclaimed Doris, good naturedly. "Come on, let's take a walk. It will be good for our nerves!

"But I'll tell you one thing," she added as they started off. "If I believed _half_ the things you do--I'd be getting out of here!"

"It's not so easy," Mildred replied, soberly. "Grandfather is a dear. It would be a shame to leave him alone. Of course he says he's going to send me back to college in the fall, and I suppose I shall go. College means so much these days."

"Yes," Doris agreed, "I'm sure it does."

"But he can't do that unless we get our motorboat up from the bottom," said Mildred. "And even after that--there are the spies."

"Spies! Always spies!" Doris laughed. "Let's forget them!"

"O.K. Let's do," the other girl agreed.

The trail they had chosen led to the beach where the mysterious male chorus had disappeared. Arrived at the beach where the waves were now racing, they stood for a time in silence. When a piece of driftwood--the broken side of a native dugout--came floating in, Mildred turned away with a shudder, her thoughts on Johnny.

Having wandered into the jungle a short distance she stopped suddenly to stare at the trunk of a tree. There, standing out against the smooth gray bark, was a small, green arrow!

"Doris!" she called. "Come here!"

"Green arrow!" Doris exclaimed, reaching Mildred's side. "What do you suppose it means?" she whispered.

"It's a trail marker!" said Mildred. "There should be others. Come on!"

There were others! Some were quite far up on the trees, while others were low. They continued the search for ten minutes, steadily finding others.

Doris was frightened and did not wish to go on. At every turn of the trail she expected to come upon a freshly made clearing, a cluster of tents and a whole army of strange warriors.

But Mildred thought of but one thing.... Perhaps they were on the road to a real discovery.

As they went deeper and deeper into the jungle, the green arrows became scarcer, and harder to find. The trail grew steeper and narrower. Thorny bushes tore at them, and once a great snake crossed their path. Unused to all this, Doris was distinctly uneasy. But Mildred's face fairly shone.

However, when they came to a place where the trail split into three narrower ones and, search as they might, they could not find a single arrow, Mildred, too, was ready to give up.

"Come on," said Doris. "It will soon be dark, and I must get back to the boat. They may want to put out, in search of Johnny and Samatan."

"You're right," said Mildred. "We must be starting back. But--I'm coming back here again!"

"Alone?" Doris stared.

"Perhaps."

The journey back to the Kennedy home was made in silence.

By the time the girls had eaten their evening meal it was completely dark. Wandering down to the beach they listened to the diminishing roar of the sea, and watched its strange blackness against the moon's golden light.

"There's a light!" Doris exclaimed.

"Yes, sir! And it blinks!" Mildred became excited.

After watching for a full minute, she suddenly threw her arms around her companion to exclaim: "Oh! Doris! That's Johnny! It is--it surely is! Sometimes he blinks his light from the ship that way--one, two, three--one, two, three! Oh, it's wonderful! Aren't you glad?"

"Of course I'm glad," said Doris. "But then--men always do manage to get back one way or another, don't they?"

"Oh! Oh, no!" Mildred caught her words. "They don't--nowhere near 'always'."

Just then Dave and the professor came down to the beach.

"We think it's Johnny and Samatan," Doris said quietly.

"Good!" said the professor. "That lifts a load from my shoulders!" He turned to speak to Mildred, but she had gone.

Ten minutes later, natives caught the dugout and hauled it far up on the sandy beach.

After receiving the congratulations of his shipmates, Johnny began flashing his light into the surrounding darkness, searching for Mildred. At last the beam came to rest on a charming picture--a girl with reddish-golden hair, wearing a dress of golden material, tied at the waist with a broad red sash. All this--against the greenish blackness of a jungle night.

"Why!" Johnny exclaimed, as he caught her hand. "The little beach-comber has turned into a golden fairy!"

"P--please, Johnny!" Mildred stuttered confusedly, "I--I just wanted to--celebrate your return from the d--dead!"

"Nonsense!" exclaimed Johnny. "I always come back. But it was mighty nice of you, anyhow, and I won't forget!"

* * * * * * * *

He was ready for a good, long sleep. His task of watching was given over for the night to Samatan's son, who was a member of the native crew. So Johnny did not return to the boat, but was shown to the guest room of the Kennedy cottage where, under a mosquito-bar canopy, with the tropical moon shining through the bamboo lattice, he slept the sleep of the just.

By the next afternoon both he and Mildred were ready for further adventure. Together, they tramped into the jungle.

"If we find more green arrows," said Mildred, fairly tingling with excitement, "where do you think the trail will lead us?"

"Hard to tell," said Johnny. "It might take us right to the spot from which the green arrow of light shines out in the night."

"And then?" she whispered.

"No can tell!" laughed Johnny. "We'll answer that when the time comes."

But would they? And what would the answer be?

After hours of searching they decided that, whatever the answer might be, the finding of it must be postponed for another day. Beyond the spot where the trail forked, they could not proceed.

"There's something queer about these signs of the green arrow," said Johnny, dropping onto a cushion of moss in the shade. "There is something we don't know about it all."

"Yes," replied the girl, "and we're going to find out what it is!"

"But not today," said Johnny. "The shadows already are growing long."

By the time they reached the beach from which the singing band had so mysteriously disappeared, the abrupt, tropical darkness had fallen. For a moment they stood looking at the dark, mysterious sea. Suddenly Mildred gripped Johnny's arm and whispered:

"Look! The green arrow!"

True enough. Seeming but a stone's throw from shore, the green arrow appeared to rise from the sea.

"It _must_ be on a submarine!" Mildred whispered.

"Wait! They're signalling." Johnny dragged pencil and paper from his pocket and began scribbling numbers. This continued for two minutes. Then, as suddenly as it had appeared, the green arrow vanished.

"Gone!" the girl exclaimed.

"Come on," said Johnny. "I want to see what they were saying."

Leading the way to a dark hollow where their light could not be seen, he asked her to hold the electric torch while he deciphered the message.

"'_We will strike_,'" he read aloud, "'_at the earliest possible moment!_'

"That's all." He stood up. "Spies strike in the dark--and without warning. I wonder what we have ahead of us!"

CHAPTER XIV AN IMPORTANT DISCOVERY

That night as he tramped the deck on his silent watch, Johnny found his mind crowded with disturbing thoughts of the significant message the green arrow had flashed over the sea.

"_We will strike_--" his mind went over the words again and again, "_at the earliest possible moment!_" Where would they strike? And who was to receive the blow? His shipmates on the _Sea Nymph_? Old Kennedy and his daughter? Or someone he never had seen?

"I may never know," he told himself. "Spies strike in the dark."

Johnny had read that during the World War, spies had swum to the propellers of outgoing ships laden with men and supplies. Hours later, with the ship far out at sea, a bomb had exploded, blowing away the propeller and leaving the ship helpless. He knew, too, that spies had placed incendiary bombs in the holds of ships, and dumped quantities of acid in the very bottom of a vessel, to eat its way through the steel.

"Yes," he thought, "and even now--in times of supposed peace--they are boring in!"

* * * * * * * *

The _Sea Nymph_ left the river and put out to sea while Johnny slept. When he awoke in mid-afternoon, they were anchored in their old position.

"How would you like to make a solo journey in the steel ball?" Dave asked when he came on deck.

"Go--go down alone?" Johnny asked, feeling a bit strange. "That--oh, that's O.K., I guess."

"I was down this morning," said Dave, "and my eyes are tired. There are some pictures I'd like to have. Conditions below are all right, and there's an off-shore breeze. We've two lines out to windward, which should hold her steady.

"What the professor would like," he went on in a businesslike tone, "is to have you go down, slowly, along that submerged cliff, stopping every ten feet to take a photo floodlight picture. That will give us a continued story of plant and animal life, down to perhaps two thousand feet."

"Al--all right," Johnny agreed. "I can do that." But for the life of him he could not still his heart's wild beating. He seemed to be hearing a voice say:

"_We will strike--at the earliest possible moment!_"

He forced his lips to repeat: "Two thousand feet, you say?"

"About that. Better get ready at once. The wind may pick up."

"Yes, it may stri--pick up," Johnny agreed a little absently.

Twenty minutes later, inside the steel ball and busy taking pictures of the wall as he stopped each ten feet, he had all but banished thoughts of the green arrow from his mind.

* * * * * * * *

But someone else really was seeing green arrows--and plenty of them. That was the granddaughter of old Mr. Kennedy--the man who for twenty years had defied encroachments of foreign interests in this happy little republic. For Mildred had gone on a hunting expedition all her own. She was hunting spies. She had started once more over the green arrow trail and, strangely enough, almost instantly had discovered the secret of its markings.

During their months together she and her grandfather had spent hours on end, tramping the jungle, and he had taught her to know all the usual signs. The trail of some great snake in the sand--the uprooted earth, where little wild pigs had been--the marks of a monkey's claws on the green sprouts of a tree--all had a meaning for her.

Knowing these usual signs, she had looked for unusual ones--and had found them. On reaching the spot where they had lost the trail on two other occasions, she noted that the next to the last arrow was low down, while the _last_, was some ten feet higher. So--to reach this last marking place--someone had been obliged to climb! In doing this, bits of bark had been broken off, leaving fresh, light-brown spots on the tree trunks.

"Now I shall look for broken bark--not arrows," she told herself.

She had not gone forward a hundred paces on the right hand fork of the trail, when she let out a cry of surprise and joy. Not only had she discovered broken bark, but up, perhaps thirty feet on a tree, she saw a green arrow.

"One, two, three," she whispered. "Perhaps that's the way it goes. One arrow down low, one a little higher, and a third, well up on the trunk!"

She discovered at once that this was just the way the markings ran. So immediately she took up the trail again.

The distance from the shore of the island to the summit of the tallest hill, was considerable. The trail, such as it was, made only by natives and wild animals, wound round and round--up and up.

The girl followed this trail for more than an hour. Then she sat down on a fallen mahogany tree to think. She was far from all her friends. Should she go farther? She, too, recalled the last message of the green arrow of light--about "striking"!

"Perhaps I can stop them," she whispered stoutly, as she rose to her feet. "At least I can try!"

Though her knees trembled, she did not falter, but marched straight on. For was she not the granddaughter of old Kennedy--hero of a hundred battles?

CHAPTER XV ADRIFT IN THE DEPTHS

All went well with Johnny on his undersea photographing trip until he had reached the fifteen-hundred-foot level. Then he called in his loud-speaker to Doris, who was directing the controls:

"Sorry, Doris. On that last, ten-foot shot, I made a double exposure. Hike me up a bit, will you, please?"

"O.K. Johnny," was the answer. To the men at the hoist she said: "Up ten feet."

"Up ten feet," the men repeated.

Johnny waited for the rise. His floodlight was on. Some strange creatures with amazing teeth, were passing, and he snapped his camera.

"Interesting place, down here," he thought. "Hate to stay down here all night, though." His leg felt cramped. He tried to shift to a new position, but at last gave it up. "No sort of place for an active person," he sighed. "Wonder why I don't go up a bit--I'd like to get this over!"

"Hey, up there!" he called into the phone. "What's wrong?"

"Sorry, Johnny," Doris drawled. "Something's wrong with the hoist. It won't work. But they'll get it fixed pretty soon, I guess!"

Something wrong with the hoist! Johnny experienced a cold chill. Suppose someone had been tampering with that hoist--had done something really serious? What then? You couldn't take hold of a fifteen-hundred-foot steel cable with a two-ton ball at the end of it, and haul it by hand like a fishline. Johnny realized all too keenly that his life depended on that hoist.

"It could have been tampered with," he told himself. This was all too true. While the boat had been in the harbor it had not been any too carefully guarded--and Johnny had been off duty one whole night! "Might cost me dearly--that night!" he thought.

To ease his mind he began watching the passing show--fire-glowing shrimps--flying snails, and a host of other strange creatures. He snapped his camera again and again.

"I say, up there," he exclaimed impatiently, "what's keeping us?"

"Sorry, Johnny. It's the hoist. We--"

Doris stopped suddenly. Johnny felt a shock--as if his cable had been struck by something hard and heavy. At the same instant the ball began drifting away from the submerged wall of rock.

"Hey, there!" he called, in genuine alarm, "what's up now?"

There came no answer. He called again, and yet again. No answer. His heart began pounding madly.

"This won't do," he told himself, savagely. "Probably nothing--just nothing at all! It--"

Then came a second, jolting shock, and--ceasing to move in a circle--the ball began drifting quite rapidly away from the rock and out to sea.

Johnny knew at once what had happened. One of the anchor cables holding the boat in place had been struck and broken.

"By that submarine!" he burst out savagely. Then as if it were right out there in the water in front of him, he seemed to see the green arrow of light, and to read:

"_We will strike_--at the earliest possible moment!"

"They have struck!" he thought. "The second cable has been broken by the added strain--and we are drifting out to sea!"

He tried to think what this meant. The hoist was broken, so he could not be pulled up. Out to sea some three or four miles were coral reefs and beneath these, no doubt, a rocky wall. Moving at its present rate and striking that wall, the steel ball might crack!

Only one cheery thought came to him at this moment. If the boat's small motor was strong enough to counteract the force of wind and current, he could be held in one position until the hoist was repaired.

Even as he thought this, Doris came back on the air: "Awfully sorry, Johnny, but something has severed an anchor cable--and then the other one broke! The hoist won't work. We'd have the motor going, but that, too, seems to have gone wrong. Keep your chin up, Johnny. We'll get you up out of there before it's--too late." Her voice faltered at the end.

Johnny found it impossible to utter a single word in reply.

* * * * * * * *

In the meantime, Mildred still was following the signs of the green arrow trail.

As she advanced, the trail grew steeper and rougher. She followed it between dark pines, where the shadows were like night, along a narrow ledge to an abrupt descent into a low ravine.

More than once, as if contemplating retreat, she turned and looked back. But always, she went on.

At last, weary from climbing, she dropped down on a flat rock in the shade and dabbed at her damp cheeks with a white, red-bordered handkerchief.

As she rested she turned her head quite suddenly to listen. All the usual sounds of the tropical wilderness--the call of monkeys, the shrill squawks of parrots, the piercing screams of jungle birds--these all were familiar to her. But did she hear some strange sound--perhaps a human call? Listening intently for a moment longer, she rose and journeyed on.

Some ten minutes later she paused once more. She had come to a spot where the trail led round a towering cliff. In an involuntary gesture of dismay her hand unclasped and she dropped her handkerchief. It fell unnoticed among some large leaves--a bit of red and white amid the eternal gray and green of the jungle.

Summoning all her courage, Mildred proceeded along the rocky trail. Like a soldier she tramped straight on until, with a startled cry, she stopped abruptly, on rounding a sharp turn in the path.

There, directly ahead, was the ancient castle that might once have been a fortress or a prison. Standing before its door and staring intently at her, was a man with a rifle. Turning to flee, in complete panic--she found herself facing another man, similarly armed.

A man in front of her, and one in back--a towering cliff above--a precipice below. She was trapped.

* * * * * * * *

Darkness came to the Kennedy cottage, but no Mildred returned to join its worried owner at his evening meal.

He ate alone and in silence. In silence he smoked his pipe on the veranda until midnight. Then he went to the house of Pean, his head native.

"Pean," he said, "she has not returned. At three o'clock, unless I come again, tell Camean to make _wanga_ with the drums."

"Make _wanga_ at three. Can do," said Pean.

CHAPTER XVI VOICE OF DRUMS

Johnny, meanwhile, was having a very bad hour all by himself. Still drifting a thousand feet beneath the surface of the sea, he awaited his deliverance--a deliverance he knew might never come.

Knowing little about the rate at which the powerless boat might be drifting, he made a guess; it should be about two miles per hour. "That gives me less than two hours," he told himself, grimly.

After noting the time, he decided to take a few more pictures--just in case.

Never before, he imagined, had such opportunity for taking undersea shots been given any living being. Moving at fairly steady speed, he passed through countless schools of deep-sea creatures, and never before had Johnny looked upon such fantastic sights.

"Like things in a nightmare," he told himself. "All heads--practically no bodies at all--some long and slim as a leadpencil, with noses half the length of their bodies. If ever I get out of this I probably shall be famous. But--"

What was this? His eyes stared at the compass. It appeared to have gone wrong, or else--

"Hey!" he called into the loud speaker, "what's up? Are we going north by east--"

"North by east is right. Oh, Johnny!" Doris apologized, "I didn't let you know, but they have the sails up, and we're traveling in a circle. We think that will keep you off the rocks. The chart is not very clear, but we can cruise around for hours if--if it is necessary."

"Hours!" Johnny groaned.

"Well, anyway--" Doris stopped, abruptly. Then:

"Johnny! You're saved! The mate just told me the hoist will be working again any minute now!"

"Hooray!" Johnny shouted. "Hooray! We live again! Boy-oh-boy!"

"Yes, Johnny,"--the girl's voice went husky, "it will be good to see you!"

Ten minutes later, Johnny was going up. Slowly, surely, the dense darkness passed. The blue black of early dawn was changing places with glorious hues, and then came the light of a rapidly passing day.

As he tumbled from the steel ball Johnny placed a box of plates carefully on the deck.

"There you are!" he exclaimed. "Pictures I'll really live to see!"

The pictures were superb--all the professor could have dreamed of, and more. "These, alone, will add greatly to the world's riches," he said, placing a trembling hand on Johnny's shoulder.

"And when you show them," Johnny grinned, "tell your audience they were taken by a ship's watch, will you?"

"I take it," said the professor with a laugh, "that you think you'd like to keep your feet on the ground, for a while!"

"Absolutely," Johnny agreed. "And in more ways than one!"

Johnny went back to his old task of walking the deck that night. There would be no more tampering with hoists and motors if he knew anything about it--and he surely would know if it happened in the night.

For some unknown reason, this night was not like others that had passed. There seemed to be a spirit of unrest in the air.

Doris, too, felt it. Enveloped in a midnight-blue gown, she wandered out on deck.

"It's ridiculous," she exclaimed. "A grand night to sleep, but my eyes just will not stay closed!"

"There are ghosts in the air," said Johnny. "I have felt them and almost heard their wings--or do ghosts have wings? There goes one now!"

Doris jumped as some swift, darting thing shot past her head.

"Oh, no!" Johnny laughed. "Only a bat. You'd think--"

He stopped suddenly to stare at the distant hills. The next instant, with binoculars held to his eyes with one hand and a pencil in the other, he was recording a message.

"The green arrow speaks again," he murmured softly. "Oh--Oh--now it's gone! Snapped right off as if a fuse had blown.

"Oh, well--perhaps it will flash again, later." He stuffed his notebook into his pocket.

"We'll be leaving here soon," Doris said quietly. "In two or three days, I think. Grandfather received a wireless today. And how I'm going to hate it." She sighed. "This," she spread her arms wide, "this has been grand! Moonlight on gorgeous waters! Strange tropical shores. Adventure!"

"And bats!" said Johnny, as one shot past his ear.

"But even they are different," she insisted, smiling.

"Yes, I know," Johnny agreed. "To go to strange places, to see new things, to find excitement, thrills, mystery and adventure--that's life!"

"Is it for most people?" she whispered.

"Perhaps not," he replied thoughtfully. "Most people like to be safe and comfortable, to go to the same places, to see the same people, do the same things. That's their privilege, of course."

"That's right, Johnny. And now--goodnight."

"Goodnight," he replied, softly.

Halfway between midnight and morning, when even the bats were less active, and the whole tropical world seemed asleep, Johnny was amazed to hear the sudden roll of a native drum, from the island. The very sound of it at that eerie hour, set his blood racing and his skin prickling.

"Drums!" he ejaculated. "What can that mean?"

For a time the weird beats were a steady roll. Then they began breaking up; two beats, a pause--one beat--pause, three beats--pause....

"Like a message," he whispered. Then with a start, he recalled the message of the green arrow--undeciphered in his pocket!

Dragging it out, he began decoding it, growing more and more wildly excited every minute.

"H--E--" he worked it out "L--P! _HELP!_"

"Someone is in trouble," he whispered. "But there are only three letters left. Rapidly he studied these out.

"_Help Mil_--"

A cold sweat broke out on his brow. He recalled Mildred's determination to follow that green arrow trail. Had she followed it too far? Had the spies captured her? Was she a prisoner? And had she attempted to get off a message on the green arrow, only to be interrupted? Or perhaps even--

"I might be wrong," he told himself. But he dared not hope.

Again there were the drums. This time a drum close at hand, on shore, thundered out. Then, from far away in the jungle came an answer, another, and yet another. It was ghostly, romantic, thrilling. Johnny's hair fairly stood on end. But what did it mean?

He caught the sound of soft footfalls. Instantly he was on his feet, all attention.

"Oh!" he exclaimed softly. "It is you, Samatan."

"Yes. The drums! They speak!" murmured Samatan. "Something--it is very bad." His voice was low-pitched, tense.

"What do they say?" Johnny asked in a whisper.

"That something very wrong. This what drums say!" The old man's voice was vibrant with emotion.

"They say Kennedy has had _bad_ done him! Natives must come. All who love Kennedy must come. And all natives love Kennedy! All night they must come. In morning they march--perhaps they fight! Much fight for Kennedy! Maybe much die!" His voice trailed off.

"Yes," Johnny choked. "Something terrible has happened. We must go, Samatan!"

"Just when it little light, in my dugout, we go, Johnny," said Samatan, quietly.

Settling back in a steamer chair the old man closed his eyes and appeared to sleep. While from the shore came again and again the vibrant rumble of the drums--tum--tum--tum--tum--on and on into the night that was marching toward the dawn of another day.

Tense with forebodings of what might be in store, Johnny waited--impatient and grimly expectant.

CHAPTER XVII MARCHING ON THE CASTLE

Old Samatan was not asleep. He was only thinking. After a time he opened his eyes wide, to stare at the dark shore where drums still beat out their message.

"Make _wanga_," he said to Johnny. "Always when trouble, my people make _wanga_--make prayer to Voodoo gods. Gods help good natives win victories."

"Great!" exclaimed Johnny. "Then we shall win!"

"Yes. Win," the old man said, softly.

Then Johnny told Samatan of the green arrow trail that Mildred had said she would follow. He told of the suddenly broken message he had picked up from the green arrow.

Thinking deeply, Samatan declared they should go very soon--at least a full hour before dawn.

"Shall Dave go, too?" Johnny asked.

"Plenty men on shore," the old man waved an arm. "We go--tell Kennedy. That all. Dave? Better Dave stay."

Half an hour later, Johnny wakened Dave to tell him what was going on. At first Dave was determined to go with them and have a hand in the affair. But after sober thought he decided it best to stay with the ship.

"The ship may be needed before this thing is over," he said.

"Yes, it may," Johnny agreed.

So, guided by native fires on the beach, Johnny and Samatan headed for shore.

Johnny was steeped in gloom as he pictured the golden-haired little beach-comber, the prisoner of unscrupulous spies.

"Nothing could be worse," he groaned. "I should have warned her never to go, alone!"

But the moment their boat touched shore, Johnny's mood changed quickly for the better. Seldom had he witnessed a more inspiring sight. In two short hours, more than a hundred, dark-faced, half-clad, natives had gathered at the call of their beloved Kennedy.

They were squatting around the fires, roasting small fish or strips of peccary meat and gulping cups of bitter, black coffee.

"They will go for a whole day on this," Kennedy told him, "and still be with us when the day is done."

When Johnny told of the green arrow's message and the trail Mildred had sworn to follow, the old man's brow wrinkled.

"I suspected something of the sort," he rumbled, "but this is worse than I figured. There may be a number of those spies--all well armed. And we--" he went on, with a touch of sadness, "these people here are not warlike. We have two heavy rifles of ancient make, half a dozen light, hunting rifles, two or three shotguns, and a hundred machetes. But these natives--" There was a rumble of admiration in his voice. "You should see what these men can do with those two-foot blades of theirs! There are two grindstones out behind the house--and they haven't stopped turning for hours!"

Johnny felt a tingle course through his veins as the old man finished. It was, he thought, like the days of old, like something he had read in a book. They were to storm an ancient castle to rescue a fair lady!

There were men among that loyal throng who knew every trail leading to the old castle.

"The men say it will take about three hours to reach the place," said Kennedy, when just after dawn, they prepared to break camp. "We shall have to march in silence, as sound travels far. I only hope," his brow wrinkled, "that these spies did not guess the meaning of those drums. I hated that. But there was no other way to get the men together, nor," he added in an undertone, "to put the real, fighting spirit into them. For more than a hundred years, the beating of these drums has meant battle!"

"And how they respond to it!" Johnny enthused.

"Yes, Johnny," the old man rumbled. "These are faithful, loyal people. Think what it would mean to have these islands taken over by a foreign power--cannon and bombing planes everywhere. If war came, think how these beautiful islands would be torn to bits by bursting bombs! Just think Johnny! Try to imagine it!"

For a moment after that, there was silence. Kennedy's voice was husky when he spoke again. "Johnny, my boy--I've come to like you a heap. Promise me, Johnny, that if anything should happen to me this day, you'll see the girl safely back to her own land where she rightly belongs."

"Nothing can happen to you," Johnny declared, stoutly. "You could handle four of those cowards, single-handed."

"Promise me," the old man insisted.

"I promise." Johnny put out a hand that was at once caught in a grip of steel.

And so they marched away into the golden, tropical dawn.

* * * * * * * *

Those on the _Sea Nymph_ were on deck early that morning. Coffee and muffins were served in the forward cabin. After Dave told what was happening on land, a silence fell over the party. Active, happy, always friendly, Mildred had found her way into all their hearts.

"Dave," said the professor at last, breaking the silence, "since that fine old man Kennedy is in a good way to lose his granddaughter--"

"Oh, but he won't!" Doris broke in. "Not with Johnny Thompson on the trail of those spies. I had a letter last week from an old friend, Marjory Morrison. She's known our Johnny a long time, and she says he's a marvel!"

"No doubt," said the professor. "But spies, my dear!"

"Spies are cowards," Doris exclaimed. "Just the same--I'd like doing something for those Kennedys!"

"Just what I was about to suggest," the professor beamed. "Manifestly, we can't sail this ship up that mountain but we can go in search of their sunken schooner!"

"Oh, yes!" Doris sprang up. "Let's do that! Anything to help!"

"I know the spot, within a mile," said Dave. "Kennedy showed me on the map. It's not over three miles from here."

"Good! We shall weigh anchor at once," exclaimed the professor. "In the steel ball, Dave, you should be able to locate the schooner in a very short time."

"And then?" asked Dave.

"One problem at a time," smiled the professor, who during his long life had solved many a problem.

Fifteen minutes more and they were away.

"Do you think we shall be able to find their sunken schooner?" Doris asked, as she and Dave stood in the prow, looking at the hills. "That depends," said Dave. "Just now, another problem interests me more."

"And that?"

"Whether that girl, who seems the very spirit of the island, ever will sail that schooner again."

"Never doubt it," said Doris. But in spite of her high hopes, she herself was in grave doubt.

* * * * * * * *

Johnny was never to forget that silent march up the tropical island trail. Before him glided a native guide. Behind him, taking each steep ascent with the quiet, steady breathing of a boy, came the giant Kennedy.

After these marched a silent throng. Their faces and machetes shining in the morning sun, they were a band of simple, honest natives, in whose midst Kennedy long had stood out as king.

A monkey chattered from a tree, but no rifle was aimed at him. A parrot screamed, and over in a narrow ravine, a drove of wild pigs scampered unmolested over the dry moss of the jungle.

"We're seeking bigger game, today," the boy thought, grimly.

Finally they arrived at a point not far distant from the turn, beyond which lay the castle. Kennedy held up a hand, and the men gathered silently about him. In low tones he gave them final instructions.

There were, he said, three trails to the ancient castle. They would divide into three groups. John Puleet, a stalwart native, with his followers, would circle the hill to the right. Teratella, another burly leader of the islanders, would go to the left with his men. Time would be given them to take their positions. When this had been done, a "wild parrot" would scream from the right, another from the left--and they would all move forward.

"We'll take the trail straight ahead, with old Samatan," he said to Johnny. "It's the toughest of them all, if we are attacked."

"O.K." Johnny murmured, gripping his light hunting rifle.

Silently, one by one, a hundred men crept into the brush. After that, save for the chirp of some small bird and the faint sound of a dashing stream, all was silent. It was, Johnny thought, the dead silence that comes before a storm.

Stooping suddenly, he picked something from among the leaves by the trail. It was Mildred's lost handkerchief. He held it out for Kennedy to see, but neither said a word.

CHAPTER XVIII THE BATTLE

Meanwhile, Dave and Doris were warming to the search for the small trading boat that had meant so much to Kennedy and Mildred.

Having found the approximate location where the little supply schooner sank, Dave climbed into the steel ball and was lowered into the deep. For an hour after that, with the steel ball always close to the bottom, they sailed about in ever widening circles. From time to time Doris called on the radio:

"See anything?"

"Yes, a whole flotilla of jellyfish," would come Dave's laughing answer. Or--"there's an ancient wreck off to the right--goes back to pirate days, I'm sure. But I don't catch the faintest gleam of a white schooner."

When at last he returned to the surface and was released from his spherical prison, he complained of eye-strain.

"Let me go down with you," Doris pleaded. "I'll be eyes for you. Together we can't fail to find the schooner. We just must get it located!"

"What do you say, professor?" Dave turned to his superior.

"What's the bottom like?"

"All sand."

"No rocks?"

"Not a one."

"O.K., my girl--in you go." The professor waved a hand, and in they went.

To the imaginative Doris, this fairyland of waving seaweed, darting fish, and drifting jellyfish was most entertaining, but she never forgot their real mission. "Dave!" she exclaimed more than once. "I see something!" A moment of excitement, and then--"No--it's nothing but a bit of coral, after all."

Then, of a sudden, a whisper reached her ear:

"One eighty--eighty-two and a half--eighty four--"

"Dave! He's back! The whisperer is back!" Doris spoke before she thought.

"Why! Hello there, mermaid!" came in words startlingly distinct.

Doris and Dave remained silent. Who could this be? Where was he? On land, or in the sea? Or on it?

For a time they heard that whispering of numbers. Then it faded, as abruptly as it had come.

As they drifted, they quietly discussed the strange whispering, but came to no logical conclusions. Neither did they sight any white schooner, resting on the bottom.

* * * * * * * *

For a long time, there on the side of the hill beneath the tropical sun, Kennedy's fighting band watched and waited.

"The signal will come," Johnny thought with a thrill. "The signal to move! And then--

"There! There it is now!" he exclaimed in a hoarse whisper.

There had come the distant scream of a wild parrot. One more scream.

"Now!" said Kennedy. "Let's go!"

"We go," old Samatan said, simply.

Johnny would have taken the lead, but the old man pushed him back. Cautiously they moved straight ahead.

Johnny sighed in relief as they reached the end of a narrow pass. That, he thought, would have been a bad place to be caught. His sense of relief was short-lived, however, for out from the wide door of the ancient castle, burst a man with a rifle. Instantly Johnny recognized him as the man whom he had saved from the grip of the octopus.

"Come on!" he exclaimed, as the man leveled his rifle. A shot cracked out, and a bullet burned Johnny's cheek. Next instant the man dodged and the rifle clattered from his nerveless hands. There had been a flash of steel, as Samatan had thrown his machete. Its point was buried in the door, just back of the spot where the man's head had been.

Dropping his rifle, Johnny executed a flying tackle, bringing the man to the ground, with a thud. Instantly two powerful natives pinned him to the earth.

"Come on!" Kennedy shouted, as the door stood open a crack. "We're going in!" His powerful shoulder forced the door so suddenly that a man on the other side of it was instantly floored. A second man--huge, fat, beast-like--lurched at Kennedy with a knife. He was felled with one blow of the old man's bare fist.

"Now!" Kennedy roared, towering over the prostrate pair. "Tell me where my granddaughter is or I'll tear you limb from limb!"

"Girl?" the fat man stammered in broken English. "Gone--gone."

"Where to?" Kennedy touched the man none too gently with his foot. But the halting reply could not be understood.

"Please, sir," came in a youthful voice from the corner, "if I may, I will tell you.

"But first I must tell you," said the youth who, until now, had not been noticed, "that I am not one of these!" He nodded at the men on the floor. "I was coming to America to join my father, and they compelled me to accompany them here."

"Is that true?" Kennedy demanded of the stout man on the floor. The man nodded.

"All right. Tell us." Kennedy's voice softened a little as he spoke to the youth. "Where is my granddaughter?"

"They took her to the submarine," said the boy.

"The submarine?" Kennedy stared.

"Yes. There is a submarine," said the boy. "They are making a survey of the sea-bottom around these islands! Don't you see," the boy seemed anxious to please, "in time of war, they shall place depth bombs and steel nets--and establish submarine bases!"

"I see," Kennedy replied in a low tone that was not good to hear. "Very nice, I should say. We seem to have stumbled into the situation at about the right time!

"But my granddaughter." His voice rose. "She is on this submarine?"

"Yes sir."

"Then," roared Kennedy, "we shall find the submarine! And if we do not--or if my granddaughter has been harmed--!" He laid his machete, sheath and all, across the stout man's throat. And the stout man turned a sickish, yellow-green. And not without reason.

"Get up!" commanded Kennedy. The two men stood up. "I'll guard them," he said to Johnny. "You and the natives search this place. Gather up every scrap of paper to be found. There should be ample evidence of this espionage. And--there is not a moment to be lost!"

"Not a second," said Johnny.

A few hours later, with three other prisoners taken by the second band of natives attempting to flee from the rear of the castle, they were back at the Kennedy cottage. At once Johnny and Samatan prepared to leave for the _Sea Nymph_.

"We'll do all in our power to find that submarine," Johnny assured Kennedy, as he and Samatan pushed off....

But Johnny could not have known, of course that the submarine had been found....

* * * * * * * *

For a long time Doris had watched the sea bottom as the steel ball moved about in a circle that ever grew wider. So absorbed had she become that her ear-phones were forgotten. When suddenly a voice broke in on her thoughts, she jumped involuntarily.

"Hey, there! I say, there! Are you there?" came in a hoarse, anxious voice. "Listen! It's important! Listen! Are you there?"

Doris adjusted her microphone, then answered, as her heart missed a beat. "Yes, we are here. Why?"

"Listen!" came in gutteral tones. "We are on the bottom, and we can't get up!"

"Try the Australian crawl," Doris laughed into her speaker. These people were good at kidding, whoever they were.

"Listen!" came in a man's voice, hoarse and insistent--even pleading. "We are in a small submarine. We are on bottom and our pumps have failed!"

"Submarine!" Doris whispered, as she and Dave gaped at each other.

"We are about two hundred feet down," the voice went on, desperately. "Something's gone wrong with our pumps, and we can't blow out the water in our compartments. You gotta help us. We have a friend of yours here and she'll tell you I'm speaking the truth!"

Doris and Dave were startled beyond description when they heard Mildred Kennedy's voice coming over the air.

"Listen, Doris," the girl's voice was tense with emotion. "I'm down here in this submarine. I blundered onto that ancient castle up on the ridge, and there were spies there. They wouldn't let me go because they--they said I'd tell what I saw. And that--that's true. I would!

"But these boys on the submarine--they--" her voice broke a little, "they're not really spies! They're just boys in the navy of their country, doing what they're ordered to do. They've been decent to me, and they'd have put me back on land if they'd dared. So--so you can't let them die like this. You just can't, Doris! Besides, I--" she choked, and could not finish.

"We won't let them die and most of all--we won't let _you_ die!" declared Dave, who had been absorbing every word. "Just you keep cool and stand by. We--we'll have our whole navy here in no time. Just you see!"

"Th--thanks, Dave ... Mil--Mildred, signing off," came in a wee small voice.

"Gee, she's a game kid," whispered Dave to Doris. Then into his microphone:

"Put that man on again," he said.

"Here, here I am," came the hoarse voice from the submarine.

"Here's what we'll do," Dave said, shortly.

"We have a fairly powerful wireless on our ship. We'll get in touch with the United States Naval Station at Port au Prince at once, and report the situation. They will send assistance--even though you're over here to help your spies! Now--give me your location--in code."

"O.K." the foreigner answered, humbly, "Here it is. 2 - 4 - 7, 9 - 3 - 6, 1 - 6 - 3 - 9, 3 - 7 - 9.--That is all. Will you please repeat?"

Dave read the numbers he had written, and the sub commander checked them again.

"Don't be nervous or frightened about the girl, here," he said. "We have oxygen enough for thirty-six hours, at least."

"I hate to think what would happen to you if any harm comes to her," Dave answered, grimly. "We're signing off and going up."

To get the Port au Prince naval station was only a matter of moments, after the steel ball was back on board.

"There's a submarine and a coastguard cutter at Santiago de Cuba," was the answer. "We will get in touch with them at once, and you can be sure of fast action!"

After a short wait came the encouraging news: "Submarine and cutter proceeding to the rescue under forced draft!"

Fifteen minutes later the _Sea Nymph_ was in motion. Dave, having obtained the grounded submarine's location, would sail to the spot and stand by to aid, if possible.

"Perhaps we'll go down in the steel ball and reach them before that sub arrives," he said.

"But Dave!" Doris exclaimed. "What can one submarine do for another on the bottom? Surely they can't raise it!"

"No--o, they couldn't. Nor could we. But then," Dave sighed, "there must be some way. We'll have to leave that to the navy, I guess."

Two hours later the steel ball rested on the sandy bottom some two hundred feet down, and within twenty feet of the submarine's dark bulk. As Dave and Doris stared out of their window, they saw a face in a port of the submarine. It was Mildred, and she was waving at them.

"Only twenty feet," Doris murmured, "and yet for the moment there's nothing we can do! How strange--and how--how terrible!"

CHAPTER XIX ON THE BOTTOM

Night was falling on the waters of the blue Caribbean when Johnny and Samatan finally reached the _Sea Nymph_, and were told of the sub's predicament. For a full hour after darkness fell, Doris and Johnny sat on the after deck. But they spoke hardly a word. They were thinking of a brave, American girl, two hundred feet below surface, in a foreign submarine.

"Johnny!" Doris gripped the boy's arm suddenly. "Is that a light--or is it a star?" She pointed out to sea.

"A light! No, it's a star. No! No! It _is_ a light! See! It blinks!"

"Dave!" Doris called. "The navy is coming!"

And so it was. As they stood there waiting, the light grew brighter and brighter. Then a long, sleek form, dark as the night, slid alongside the _Sea Nymph_.

"Ahoy there!" a voice called.

"Ahoy!" Dave echoed. "We'll send our small boat for you at once"

Ten minutes later, the young commander of the American submarine was on board.

"What's the situation?" he demanded, briskly.

"They're down here, about two hundred feet," said Dave. "Their pumps won't work and they can't get up!"

"That's it, eh? It sounds bad." The young officer's voice was somber. "I suppose you assumed we had a diver on board, and--until three days ago--we did have. But now he's in the hospital with a raging fever!"

"Might I inquire," the professor asked, slowly, "what a diver would do?"

"Certainly," said the officer. "We have three hundred feet of hose. Somewhere on the side of their sub, if it's anything like ours, is a short piece of pipe with a thread on it, to which our hose could be attached. After that--when they have opened an inner valve--we can pump in enough air to float them. But without a diver--"

"I," said the professor, "am a diver. Have you the equipment?"

"You?" The young officer looked at the aged professor admiringly, but without making a reply. All eyes were focused on the dignified old man.

It was Dave who best understood the situation.

He knew the professor had made many a trip to the bottom of the sea in a diving outfit, but that had been years before. Now he was a frail, old man. "The pressure at two hundred feet is terrific," the boy thought. "And his doctor has warned him--even about going down in the ball! He must not go."

Still Dave remained silent. He was thinking hard--thinking how even in life's twilight this splendid old man displayed a glorious courage.

"I must go down." It was the professor's voice. "It is my duty. Those are young people with life before them. They must not be allowed to perish."

Still the young officer did not speak.

"All right, Professor," Dave said huskily. "But first--give me an hour! I will try something. If I fail--then your turn comes!"

Slowly the professor grasped Dave's hand.

In a few precise words, Dave outlined his plans. Then he leaped toward the steel ball. With all possible speed he was bolted in, lifted over the rail, and lowered slowly into the ominous, black waters.

Never before had he been down at night. The spectacle that met his eyes as he sank, was surprising almost beyond belief. The whole sub-sea world seemed on fire. It was like being out in a moonless night, surrounded by billions of fireflies.

As his eyes became accustomed to the bizarre scene he was able to distinguish individual specimens from among the myriads of luminous creatures that crowded the waters. Here, like excursion boats all aglow, a score of jellyfish floated past. There, a throng of shrimp stood out in dark outline against the background light, suddenly darting frantically away as some great fish with bright spots along his sides gave chase. Casting off balls of illumination, the shrimp were lost to sight in a flare of light.

But there was little time for such thoughts, as this underseas mission concerned the lives of nine young people. A sudden storm would spell their doom....

Dave had asked for an hour, and he must save the professor from taking so great a risk, if possible. No less experienced person--not even Dave--could safely descend to such depth in a diving suit....

Suddenly he saw the light from the sub's porthole, just before him.

"Steady!" he said into the mike. "Doris--tell them to stop lowering, and swing me to the right about twelve feet."

Instantly they obeyed his orders and for a time, he studied the sub. Then he saw what he had sought--the threaded end of pipe for letting in the air. Once again he had his position changed. Now he was close to the bit of threaded pipe. But the dangling air hose from the sub on the surface, still was several feet away. More orders.... More moments.... and every second counted.... At last the steel ball rested on bottom. The sub was six feet distant, and now the hose dangled directly before his window.

What Dave hoped to do was to seize the screwcap at the end of the hose with the pincherlike affairs attached to the outside of the steel ball. Then, by twisting his pinchers round and round, he would try to attach the hose to the sunken submarine.

Could he do it? His heart sank as the force of a wave far above, drew the steel ball off the bottom for a moment.

"I--I've got to do it! I've _got_ to," he muttered.

Once again his hand was on the lever. It rose, slowly, as the hose before him swayed.

"Back a foot," he called to Doris.

Back he slid. "Now," he breathed. There was the hose and screwcap, and there were his pinchers. Swiftly, skillfully, he manipulated the lever, and, by a fortunate providence, caught the cap just as he should.

"Now," he breathed.

But again there came that sickening lift and swing--and one crash of his window against the sub, would spell his doom.

Now he was on bottom again. A move--a second move--then a third--and he was back in position. Now--

"No," he breathed, desperately, "not this time."

For again came that sickening lift.

* * * * * * * *

In the meantime a coastguard cutter had anchored close to the _Sea Nymph_ and an officer came aboard.

"I am Major Braden, of the Marines," he said, bowing to Doris, Johnny and the professor. "I'm on extraordinary duty just now--watching these waters. I used to be in command when we occupied these islands for military purposes, and I understand you've located a foreign submarine."

"And six spies, now held captive on land," Johnny added. "We took enough maps and reports from their hangout, to start a secret service all our own!"

"Good! Great! A real service to your country, young man!"

"But the sub's still on bottom," Johnny added, "and we're trying to raise her now. They--they've got one of our good friends on board!"

"I'm sure you'll succeed," exclaimed the Major. "And when that sub breaks water--we'll have three, six-inch guns trained on her. She'll not escape," he concluded a little grimly.

* * * * * * * *

For a full quarter-hour, Dave struggled in vain to bring the threaded pipe on the sub, and the screw-cap at the end of the hose, into exact position. At one time he actually turned the cap, and felt it catch. But it would not turn further.

"Started wrong," he murmured. "Threads are crossed. Must take it off at once."

Ten seconds of struggle and he was back where he had started. His heart sank. Should he give up? He closed his eyes to think--and saw the professor's frail, kindly face before him.

"No!" he groaned. "I won't give up!"

Slowly, carefully, he maneuvered himself into position. The lever rose slowly, and glided forward. He gave it a turn. It stuck. Deftly he twirled his lever; 'round and 'round it spun.

"Now!" he breathed. He gave the lever an experimental tug. _The cap held firm._

"Try it!" he fairly shouted into his mike.

Ten seconds later, the hose hanging loosely before his window, twisted and writhed like a snake. It was filling with air. He watched the spot where it joined the pipe on the sub. Should bubbles appear, all his work was lost. Ten seconds, he watched. No bubbles. Twenty--thirty--forty seconds. Still no bubbles.

"Hooray!" he shouted hoarsely. "Hooray! We win!"

And from the sunken sub came an answer:

"It is good! We are getting air!"

After having his steel ball moved to a safe distance, Dave settled down to watch. Had they won? Would the sub really rise?

Fifteen long, tense, minutes passed. Then, like a giant fish which had been asleep on the bottom, the dark bulk before him began to stir.

"Thank God!" Dave exclaimed, fervently.

A moment more and the sub rose slowly toward the surface. And, like a cattleboy driving the cows home at eventide, Dave followed in his steel ball.

True to the Major's promise, powerful lights and capable-looking guns were trained on the sub when, with a rush, she broke surface. But there was no need for that. The members of the youthful crew were too glad to escape death on the bottom of the sea, to offer any resistance to capture.

The first person to appear above the sub's deck was Mildred. Awaiting her in the Tub was Johnny, and how he greeted her was a sight to behold. Some time later they sat on the porch of the Kennedy home--Dave, Doris, Johnny and Mildred.

"Well, Johnny," said Dave, "our work beneath the very deep sea is done. We'll collect a few specimens--turtles, crawfish, and bright, tropical fish close to the surface--then hoist anchor for New York!"

"New York? Where is that?" Johnny asked dreamily.

"It's an ancient Dutch colony," Dave chuckled.

"Oh, yes! I remember!" said Johnny. "I think I'll not go there, if you folks don't mind." He hesitated.

"Mildred tells me she located their motorboat while she was in the submarine. Major Braden thinks we've done a brave deed or two and put him in a good way to clear up this spy business--so he's going to repay us by helping bring the schooner to the surface. But of course," he drawled, "there will be a lot of work to be done after that."

"And you'd like to stay and help" said Dave. "I don't blame you. I'd like to stay myself. Well, old son, all I can say is--go ahead and God bless you!"

"I'll be back in the States in two or three months, I guess," said Johnny. "I--I'm sort of thinking of going to college. College is wonderful for just anybody!

"I hope you come back to these waters with the steel ball," observed Johnny, after a time. "I'd like to have one good, long, look for old Samatan's treasure chest."

"Oh! That?" said Dave, with a short laugh. "Probably just a myth. But if we ever get back--you shall have a try at it, I promise you!"

* * * * * *

Transcriber's note:

--Copyright notice provided as in the original printed text--this e-text is public domain in the country of publication.

--Obvious typographical errors were corrected without comment.

--Dialect and non-standard spellings were not changed.