When he gained a full and nearer sight of the Pirate Shark, Mart's courage all but failed him. For a moment the gigantic fish seemed to hang poised in the water above and beyond him, some twenty feet away; what its actual size was Mart could not guess, in the dim and blurred light, but there could never be another such shark as this in all the oceans!

Huge, cruel-eyed, with its mouth showing as he looked up at it, Mart never forgot the horror that seized him at his first face-to-face meeting with the Pirate Shark. He thought of a thousand things in that one moment—the uncanny cunning of the terrible fish in first cutting him off from all help by biting through his lines, poor Bob waiting up above in agonies of suspense, and above all, the awful fact that unless he conquered quickly, he would suffocate.

Still the shark hung poised above him, the immense body motionless except for the gently-waving fins and tail. The big dorsal fin was hidden from him, so he could not see whether it had been pierced by the bullet or not. But he must act, and act quickly! What should he do?

In order to get at the monster shark with the kris, he would have to expose himself. If the brute was cunning enough to cut his lines, he would be too wise to attempt an attack while Mart stood in the wedge-shaped opening of the wreck. There, he could not reach the boy, and would realize it.

Mart wasted no time in hesitation. He was running a terrible risk, for once the shark butted into him or struck him with its tail, he would be flung off his balance and would be lost. But remembering his great lightness in the water, remembering how easily he could leap out of danger, he stepped forward confidently from his shelter, the kris held ready.

No sooner had he done so than the shark began to move. Gradually, with a terrible slowness, the huge shape came forward; the impulse to leap back to shelter was horribly strong, but Mart resisted it.

Around circled the shark, exposing its full length. Mart trembled at the sight, for it seemed to him that the brute must be far longer than the thirty feet which Jerry had assigned as its size. It stretched out quivering in the depths, ghostly, ominous; and most terrible of all was the silence that prevailed over all things. Mart wanted to shout, to yell for aid, and could not.

Almost without warning, the great bulk swept around and came at him, twisting about so that the gaping mouth could nip him as it swept past. But Mart was ready; every nerve and muscle in his body was tensed up to the highest pitch, and as the shark lunged forward, he swerved sharply back to his shelter.

None too soon, indeed. The gray bulk swept down on him in a great swirl that almost flung him off his feet; as he reeled, catching at the corner of the wreck for support, he saw the rough, mottled skin shoot past hardly a foot away. Mart swiftly jerked up his kris and lunged forward with all his strength.

He felt the keen weapon shear into the brute and jerk him out, but he grimly held to his grip. Something struck him and sent him staggering; then he had pulled the kris free. Barely had he done so when the shark's huge forked tail drove past his head in a lash of foam and blood, and Mart reeled back into his shelter. The sides of the wreck caught his shoulders and kept him upright, fortunately.

He noticed a slight roaring in his ears, and knew that the air was beginning to get bad in his helmet. He pressed his diving dress and forced up some of his remaining supply. Peering out, he could not repress a thrill of exultation—he had won the first round!

Yet it was a strange and awe-inspiring sight that met his gaze. Tingeing the water a dim red, the immense fish was tearing to and fro in wild fury, lashing across the entrance like lightning, drawing the water in swirls and whirlpools that came near to dragging out Mart despite his grip on the wreck. He felt even the old ship tremble beneath the fierce blast of water, while the huge gray shape flashed down and across and up, back and forth, in terrible spasms of rage. But after it trailed that thin stream of red, and Mart exulted.

"By golly, I've got to finish this thing quick!" he thought vaguely, for the roaring in his ears had increased, and it was hard to fill his lungs with the vitiated air. "If I can only settle him, I can cut off these weights and take a chance on shooting up to the top. It'll be a mighty slim chance, but it's all I've got."

Rendered desperate by his fear of suffocation, which was even greater than his fear of the Pirate Shark, he advanced to the edge of the opening with a resolute determination to take any chance that offered. Nor was it slow in coming.

Down swept the shark with a rush, flicking in its tail as it passed, and Mart leaped back only just in time to avoid it. But he saw the brute's purpose now—to try to suck him out with the swirls of water, or to strike him over with its tail, and as he eyed the dim gray shape that was circling around for another rush, he made ready. He must strike as the huge body flicked past—and he must leap back before the tail could get to the opening!

That meant only one thing. He would have no chance to pull out his kris this time. Everything would depend on the one sure stroke, which must be a death-wound. If not, the kris would be carried off in the shark's body, and with his little sheath knife alone left him, he would be helpless.

"Got to do it!" he thought dully, for now his ears were paining, and he began to feel as if his nose were about to bleed. He was gasping for air, and forcing up newer air from about his legs and body only relieved him slightly. "Got to do it this time, or lose out!"

All the water seemed faintly hued with crimson now, and he knew that his first blow must have worked considerable damage. The shark had dashed off until he could only see it dimly—a monster shadow that darted smoothly but erratically about in the distant depths, as if working itself up to a greater fury. Then it swung about in one wide sweep, and began to grow plainer as it came down upon him.

Its speed was appalling. During his instant of waiting, Mart's courage almost failed him; it seemed impossible that he could strike and leap back in time to avoid the flashing tail!

Nor could he, as it proved. The monster fish drove in upon him, turning as it came, its bulk seeming to fill all the space above and to crush him back upon the wreck; then Mart, never giving an inch, shoved his flame-bladed kris forward, saw it go home to the hilt in the gaping mouth of the Pirate Shark, and then was swept from his feet.

He went down with a rush in the tremendous swirl of waters, being drawn along the side of the wreck for a little space; but the fall proved to be his salvation. As he struggled feebly and vainly to gain his feet, he could see that everything was gone crimson around him. Through the bloodstained waters lashed the whiplike tail of the Pirate Shark, beating with terrific force against the wreck; the fish, blinded by its own lifeblood, was trying to find its enemy, and a single stroke from that tail would have finished Mart forever.

He lay quiet, huddled against the wreck, but now there was little fear of the Pirate Shark in his heart. Whatever the results of that final blow had been, nothing now mattered except the terrible pains that had come upon him. The air in his helmet seemed to poison him, his throat and lungs were on fire, and he knew that he was bleeding at the nose.

"By golly, this is awful!" he muttered thickly.

He determined not to give up without a last struggle, however. He still had his sheath knife, and he could cut away his weights and shoot up. Though it would be dangerous, both because of the pressure and because of the Pirate Shark, he spent no more thought on it but drew his knife and tried to rise.

This was no easy matter, so evenly was his weight adjusted, but he finally managed to get up, leaning weakly against the side of the wreck. His head was buzzing madly, and it was difficult for him to see anything because of the cloud of blood and stirred-up slime that filled the water.

He could see nothing of the Pirate Shark, but that did not matter now. Managing to get out his knife, he tried to stoop over and cut away his shoes. To his terror, he lost balance again and fell weakly forward, unable to stop himself. He was gasping and fighting for breath now, but there was no good air for him to breathe. He felt dimly that he was gone.

He had no strength; still he fought up to his feet once more, savagely determined not to give in to the suffocation, trying vainly to rid himself of the helmet. But he had dropped his knife, and dared not stoop for it for fear he could not regain his balance.

Suddenly something flickered across the glass window, and he gasped out a broken laugh, thinking it a snake. Snakes would trouble him little, after battling with the Pirate Shark! But was it a snake? It stayed unaccountably still; then it began to jerk forward and back most strangely, switching against the glass before his eyes. He put out his hand and touched it—rough hemp! Then he saw that a piece of metal was fastened at the end, and was bumping against his legs. It was a rope.

"Good old Bob!" he thought, as a momentary wave of coherence restored his brain to itself for an instant. "I've got to fasten it—don't believe I can hold on very long!"

However, the trailing end of his own life line was still attached to his belt. Hauling it in, he managed to get the two lines knotted, then gave the four pulls to "haul up!" He perceived the line tighten immediately, when a terrible gasping for air seized him and shook him; he tore at his diving suit with his hands, a spasm of agony making him reckless whether he let in the water or not. But fortunately the rubber-cloth was stout.

His frantic efforts had exhausted what little oxygen was left to him. He knew faintly that the wreck had seemed to drop away from him, that he was swinging up through the water—and just as the water seemed to be growing lighter, everything went black before his eyes, there was a rush of stars, and he knew no more.

Up above on the landing, Bob was pulling away desperately, with fear in his heart. At one side lay the figure of Jerry, still in diving dress but with helmet removed. The old quartermaster lay very still and white, but Bob had no chance to work over him. When Mart's line had parted and that terrible shadow had appeared down below, Bob had almost given up. Then he had leaped into energy, for he knew that now Mart's life depended on him alone.

He had swiftly cut away Jerry's back-weight and attached it to a line, which he lowered, swinging it back and forth in the hope that Mart would see it. The under-water battle had lasted only for two or three minutes, although it had seemed an age to poor Mart, and now Bob was hauling up with all his energy. He had seen the dim shadow shoot off, leaving a great trail of blood, and he knew that Mart must be hard pressed for air; as he pulled, he prayed that the shark would not return until his friend was safe.

With a sob of relief, he caught the flicker of the copper helmet in the water, and finally got the limp form to the surface. Pulling Mart in was a hard matter, but it was finally accomplished, and Bob fell on the helmet and unscrewed it with trembling hands. Mart's bloody face and ghastly pallor struck him with cold fear, but he went to work at once to drive air into the contracted lungs, hoping against hope.

How long he worked over the unconscious figure he never knew. He shouted again and again for Ah Sing, and when at length the affrighted Celestial appeared at the top of the ladder, Bob sent him for some stimulant. Ah Sing vanished, and a cry of joy broke from Bob's lips, as he saw a faint color come into Mart's face and ebb out again. Mart was alive!

Bob labored furiously, and when Ah Sing showed up with a bottle of alcohol, he said nothing but rubbed Mart's face and neck with the fiery liquid. Presently he was rewarded by a twitch of Mart's eyelids, a little more color came into the faded cheeks, and then the gray eyes opened and looked up into his.

"Look out—he's coming!" whispered Mart, his hand going up and clutching Bob's arm.

"It's all right, old boy," cried Bob, tears running down his cheeks with the relief that gripped him. "You're safe—take it easy!"

Up above them, Ah Sing burst into a frenzied chattering, then rushed away, but neither boy noticed him. Mart lay motionless, looking up into Bob's eyes and slowly feeling strength come back to him as the reviving air found its way into his lungs.

"I got him, Holly," he gasped weakly. "Did you see him?"

"Sure!" returned Bob. "Keep quiet, now. Don't try to talk. You're not hurt, are you? Nothing more than the air?"

Mart shook his head. After a moment he managed to sit up with Bob's assistance, and saw the motionless form of Jerry. Before he could speak, Bob restrained him.

"I haven't had time to look at him yet, Mart. I—I guess I feel kind o' weak myself—"

"Seamew ahoy!" came a hail. "Where are you, Bob?"

"By juniper!" gasped Bob, jumping up. "It's dad!"