"But, Mart!" Poor Bob's voice rang out in terror-stricken accents. "Jerry'll be drowned before you can reach him!"

"Shut up!" crackled out Mart, snapping his wrist-bands close. "He won't either. When the air hose is cut, that helmet valve closes automatically. Jerry's down there, an' he can't get up, that's all. Hurry up with that hose!"

Bob fell to work again, his fingers trembling. Mart got into the big shoes and laced over the flaps, for he knew that every second counted, but at the same time he must overlook no slightest item in his dress.

Never had his mind worked so swiftly as now, when the danger call came. It had occurred to him to drop over a weighted line, but he knew that Jerry might be unable to see it, and they were not sure of the quartermaster's exact position. In the same brain-flash he realized that Jerry would have some minutes of life, due to the air contained in his inflated dress; there was time for him to get down with a spare line and get Jerry up, if he acted promptly. So he had acted.

He had pictured in his mind the scene below, with that three-foot kris sticking out from the side of the wreck. The instant those bubbles appeared, he knew there was danger; and the instant he hauled up the clean-severed ends, he guessed that the line and hose had brushed against the keen kris and had been parted. Bob's startled cry had appalled him for an instant, but they had seen no shadow in the green depths, and he leaped at the true solution without hesitation.

"Get that helmet screwed on, now," he snapped, seeing that Bob had connected the air hose. "You keep your nerve, old scout! Everything depends on you, up at this end, so don't get flustered. Chase up and get a coil o' rope. I'll send Jerry up to you first. Haul him up slow, remember."

Bob, who had recovered his nerve under Mart's apparent calm, dashed up the ladder and was down again with a coil of light line. The helmet was screwed down tightly, and Mart pressed his chum's hand warmly. Then, taking one end of the spare line and knotting it around his waist beside his own life line, he drew his sheath knife in case of emergency and stood waiting for his dress to inflate.

He had concealed his own fear behind his frantic haste, and now he did not hesitate to admit to himself that he was afraid—and very much afraid, too. Oddly enough, the thought of the Pirate Shark did not cause him any great concern. While all during the voyage he had looked forward to diving, now that he was about to step off into that forty feet of water he would have given anything in the world to be able to stay up above.

But the thought of Jerry drove him steadily to the task. Picturing the old man down in the depths, hoping agonizingly for some shred of help from the two boys to whose hands he had trusted himself, Mart resolutely set himself to conquering his fears. The life of a man depended on his keeping up courage and on his remaining cool-headed. When he felt that his dress was full of air, he looked at Bob through the thick glass of the side-plates in his helmet, then sat down and resolutely lowered himself over the edge.

He very nearly overbalanced in doing so, for, in order to counterpoise the forward weight of the big helmet, the weight on the diver's back is five pounds heavier than that in front. The instant his legs were in the water, however, the terrible weight of the leaded boots was gone.

A final glance at his chum showed him that Bob, now steadied down to desperate work, was turning the big wheel with one hand and holding the lifeline in the other, ready to pay it out. At that, Mart gathered up all his courage, sidled off the landing, and let himself drop.

For an instant the sensation was terrible, as he saw the green water closing over him, and the sunlight dimming overhead. Then an almost imperceptible jerk, and he knew that Bob had stayed his fall downward, and was lowering him more gradually. He had no fears as to Bob's capability, and after that first instant he slowly collected himself to the task in hand.

He forced himself to look downward, for now he found that the water was growing darker about him, and he could feel it rushing past his bare hands. The touch, strangely, gave him courage; the water was very warm here in the lagoon, and it was something tangible, something that offset the cold dread of the green dimness rising up at him.

Suddenly he felt a determined tug at the lifeline about his waist, and as this was the usual code query as to how he was, he gave Bob a responding tug. He was getting deeper now. Without the slightest warning, he found that he was beginning to see things around him.

A fish darted past, almost flicking its tail against his front glass. Then a long streamer of seaweed rose at his right, frightening him at first in the belief that it was a snake. And with that, marine life was all around him, there came a shock—and he knew that he had reached the bottom, eight fathoms down!

Beyond a slight ringing in his ears, he felt no unwonted sensations. All about him was marine life—shells and slime and solid coral underneath his feet, with queer things that seemed to slide away from his presence. There was a little seaweed, but not much; sponges, sea fans, and several tiny writhing octopi that shot away and vanished in the obscurity. He could distinctly hear the strokes of the pumps, regular and steady.

"Good old Holly!" he thought. "But—this ain't getting Jerry."

He realized that as there was no wreck in sight in front or to the sides, and as the landing-stage of the Seamew had been directly over it, he must be facing away from the wreck. So far, he had not moved. Now, as he tried to turn about, he found himself bounding up several feet, and laughed to himself as he remembered Jerry's lessons.

But he had turned about—and the scene before him made him start back in awe and amazement. Hardly ten feet away from him was the wreck—a great dim shape with streaming sea growth and barnacles that rose more like a huge rock than anything else. A trifle above the level of his head flamed out a little silver line of light—it was the kris, protruding handle outward from the barnacled wood. But where was Jerry?

Then he saw, and moved forward with a terrible fear lest he had been too slow. The kris was stuck in the wreck at a corner, where the huge mass had split apart and had made a V-shaped opening. Just inside this lay the motionless form of Jerry, who must have become insensible from lack of air. Beyond a doubt he had penetrated into the opening, and as he did so his hose and line had caught on the kris and parted. The very weapon he had counted on for safety had betrayed him!

As he moved forward, Mart took precautions against the same danger, by pulling out the kris and sticking it into the wood again farther ahead. Then, with that strange lightness that divers feel, he leaped forward, clutching at his spare line. Swiftly drawing his knife across it, for he had no time now to untie knots, he caught the end under Jerry's shoulders and knotted it. Looking down into the glass of Jerry's helmet, he could make out that the old man's eyes were closed, while his mouth was open and was feebly gasping for air.

"By golly, I just got here in time!" thought Mart with a quick breath of relief. "He'll have to go up first, I guess. Bob can't haul us both."

With that, he separated the spare line from his own, and tugged it four times. Bob must have been in desperate fear, for he never paused to reply, but the form of Jerry rose almost at once.

Mart could still hear the pump-strokes going, however, and the air he breathed was fresh and pure. He thought of Bob, pumping with one hand and hauling up with the other, and at the same instant he thought of the four mutineers ashore. What if they had seen the whole affair and were to come out in their boat and recapture the ship?

At the very thought he felt the perspiration stand out as he gazed dully at the swaying figure of Jerry which was slowly vanishing above him. However, there was no use speculating, he considered. Little by little the form of Jerry merged into the flickering lights and shadows overhead; staring up, he could perceive the darker shade of the yacht directly above him.

"Well, I might's well take a look at the treasure!" he thought suddenly, and with that turned to the wreck. Cautiously making his way into the V-shaped opening where the rotted ship had fallen apart, he perceived that her outlines were gradually taking shape to his eyes.

She was lying directly on her side, the decks rising straight up from the rock bottom. Ahead and behind him there were projections from her decks, no doubt the forecastle and high poop of other days. She seemed to be split well asunder, for the opening was a good five feet across, and without hesitation Mart advanced into it.

As he did so, he paused, in wild apprehension. The pump-strokes had ceased! Then he grinned, with a sigh of relief; of course Bob would have had to quit work in order to get the body of Jerry over the landing, and unscrew his helmet so that air might reach him. When the pump-strokes began again, he could go up.

Mart glanced around curiously. The hold of the ancient ship was dark, and he could see nothing, for the light down here was dim, rendering all things distorted and indistinct; this his thick glass-plates did not tend to help, but a moment later he became aware of something like a box that protruded on his right, and remembered what Jerry had said about a chest of treasure being in sight.

He had sheathed his knife while sending the quartermaster up, and now he drew it and shoved the blade against the box. It seemed of great weight, for even in the water it did not move under the shock. Then he kicked it with his heavy boot, and saw it shake and shatter. The wood must be pretty rotten, he reflected, and with that he kicked it again.

"Well, I'll be switched!" he gasped, starting back. Not only had the box gone to pieces, but pouring out from its shattered corner came a stream of gold coins! That they were gold he did not doubt for a moment; even in the semi-darkness they gleamed and shone ruddy yellow, pouring out and out until they covered even the high soles of his diving boots.

"Thunder! I've struck it!"

For a moment he stared down, unable to move. Then he felt a little wave of pure air sweep around his face and heard the pumps begin to click again up above; until then he had not realized that his air was becoming vitiated. But he paid no attention to anything but the stream of yellow coins that were settling down over his feet, and neglected the fact that now he could ascend.

Gold! With the word ringing through his brain Mart leaned over cautiously, so as not to lose his balance, and stirred the heap of coins with his fingers. He wanted to take some of them up, but had no pockets. Going to his knees, he began to stuff the coins wildly under his belt, under the broad straps of his shoes, even forcing some beneath the weights of his chest.

While he was doing this, he suddenly felt tug after tug on his line—frenzied pulls that woke him from his gold-fever instantly. What was wrong? He answered with one "all right" signal, but still the tugs continued, at both lifeline and air line. Concluding that he had best ascend, in any case, he cautiously emerged from the opening until he once more stood outside the wreck.

He put out his hand toward the kris, meaning to take it up with him; then his heart seemed to stop beating and he stood frozen with horror. What was that dim, vague shape sweeping past, up above?

Mart stood gazing upward, unable to move as the realization of his terrible position flashed on his mind. The long, tapering shadow told its message only too clearly. The Pirate Shark had returned—and he was trapped! Now he understood the meaning of those frantic tugs. Bob had seen the shadow and had tried to warn him. Too late!

With a groan of agony, Mart drew back into the opening. He remembered what old Jerry had said—that so long as a man had his back to something, kept on his feet, and had a weapon, he was all right. Therefore, he must not try to go up, for then the shark could grab him with ease.

Cold sweat stood out on his forehead. What was it Jerry and the others had said about the Pirate Shark always nipping the air hose first? Poor Mart trembled as he still stared up, in hope that the shark might have flitted past and would not return. Again came Bob's frantic tugs, and on a sudden Mart felt calmness flood into his brain, and he reached for his air hose.

"By golly, I've got a fighting chance and that's all!" he muttered, then his lips clenched.

He pulled the air hose twice, then twice again, with the signal for more air. He repeated it, for he knew now what he must do. To attempt going up was impossible; the shark would cut his line, and then come down to finish him. Therefore he must get all the air possible—

"Ah!"

A little click behind his ear, and the noise of pumps stopped. A flicker of the dim gray shape above, then it became larger, more firm of outline. Down through the water curled the air hose and lifeline, bitten through, and Mart had a vision of the tremendous fish as it flitted past overhead, turning in a great curve. The sight was paralyzing. Then Mart gripped the kris, tore it from the barnacled wood, and whipped around to meet his enemy. He had no way of getting up to the surface, his air-supply was limited—but he would not give up without a struggle.