In the centre of this was a sight that made his heart jump and then beat wildly. Strewn in every direction were big tusks of yellow ivory, evidently lying just as they had been dug from the ground.

Rob was still contemplating them when his eye caught the flutter of a rag of cloth at the edge of the open s.p.a.ce. Attracted by a curiosity he could not account for, he made his way toward it. If the sight of the ivory had made him jump, what he now saw sent a chill of horror down his spine. The rag that had fluttered had been part of the clothing of what had once been two men.

Both lay close together, their bones showing where the cloth had worn away under Time's finger. A pair of rusty pistols lying by each showed how they had come to their death. The whole tragedy was as clear to Rob as if he had seen it:--the quarrel between the two ivory stealers, the duel with the pistols, and the death of both combatants beside the treasure pile they had done so much wickedness to acquire.

"Truly that figure in the deck house is avenged," thought Rob, gazing with horror-stricken eyes at the things before him. "Death was indeed the wages of sin in their case."

Turning from the grisly relics of that far-off duel on the lonely island, Rob fell to examining the ivory. There was a large quant.i.ty of it.

"It must be worth an immense sum," he thought.

But in the very moment of his triumph, Rob suddenly recollected what, in his excitement, he had entirely forgotten for the moment. He was a castaway on a strange, uninhabited island, with only a few tins of beef between him and starvation. Thirst he did not fear, for close to where he had struggled ash.o.r.e was a spring of sweet, cool water.

Rob made his way back to the beach and the boat. Inside the boat he now noticed what had hitherto escaped his attention. There were several hundred feet of light rope which seemed to be still in fairly good condition. There was, too, a pair of oars. At the same moment the boy was seized by a sudden idea. He could get away from the island, and in a boat, too!

His Boy Scout training had made him fertile in ideas, and if the present one succeeded it would mean his escape from a terrible fate.

Ensign Hargreaves and Mr. Barr looked sternly at each other.

"There is only one man who could have taken that lever," said the ensign.

"And that is who?"

"The rascal Barton."

"But for what possible object?"

"I cannot think unless he has hidden it and will only give it up as the price of his liberty."

"But if he keeps us down here, he will die, too."

"He is playing his life against ours and he holds the cards."

"Not for long. Come below at once. We must act quickly. There is a chance he still has it on his person."

Down the stairs they ran, leaving Merritt at the wheel with a sinking feeling of fear clutching at his heart. If Barton, turned desperate, had hidden the key and would not reveal its hiding place, it meant that they must remain in the depths till death put an end to their sufferings.

In the meantime, the ensign and Mr. Barr, both excited, had rushed through the cabin and toward the engine room. As they approached the door, it was slammed and a pistol thrust through a small hole in it, which had been cut for ventilation.

Then Barton's voice came ringing out:

"Don't come a step closer unless you want to get a bullet in you."

"What's the matter, man, are you mad?" exclaimed Mr. Barr.

A shriek of demoniacal laughter was the sole response.

It sent a shudder through everyone who heard it. The man was mad, violently insane. The seeds of lunacy, which had been germinating in his brain for a long time, had burst forth into a terrible harvest.

"And on that man everyone of our lives depends," breathed the ensign.

Then in a louder tone, which rang with authority:

"Barton, did you take that ascending lever?"

"Yes; ha-ha-ha! It's a good joke on you! You thought you'd put me in prison, but now we'll all die together."

"Barton," pleaded Mr. Barr, "be rational. Return that lever and you shall have immunity."

"It's too late now!" screamed the demented wretch. "We'll all die together in the depths of the sea, where dead men's bones rot and the fish eat their eyes out."

A hasty consultation followed between the ensign and Mr. Barr. The man was undoubtedly violently insane, and there didn't seem a chance in the world of dislodging him from his position.

The situation was the more serious from the fact that the fresh air devices were not working properly and the air inside the submarine was already getting noticeably stale and foul.

"We must rush that door; it's our only chance," declared the officer in a whispered voice.

"But he is liable to shoot," objected Mr. Barr, eying the blued-steel muzzle of the revolver which was pointed threateningly at them.

"It cannot be helped. It means death in a fearful form if we do not dislodge him from that position, and a man in his condition cannot listen to reason."

"Well, what do you propose?"

"That you start talking to him to distract his attention, offer him money or anything to give up the lever. Then I'll watch my chance and rush in on him; thank goodness, that door has no lock on it."

"Barton!" said Mr. Barr, in a resonant voice.

"Well?" snarled the lunatic.

"Be calm now and listen to reason. Is it money you wish?"

"No, blood! Human lives!" shrieked the maniac.

At precisely that instant, like a projectile from a gun the ensign's powerful body shot forward. Crash came his solid one hundred and eighty-five pounds against the door.

At the same instant there was another crash, the sharp crack of a revolver! In that confined s.p.a.ce it sounded terribly loud.

"He's shot him!" cried Mr. Barr.

But Barton had done nothing of the kind. The attack had been utterly unexpected by him, and as the door banged against him with terrific force, he had been knocked down. As he fell the revolver exploded; before he could pull the trigger a second time the powerful young officer of Uncle Sam's Navy was upon the man. Barton fought like a wildcat, and with the superhuman strength of those afflicted with insanity.

At last, however, he was overpowered and, raving incoherently, was tied hand and foot and carried out to the cabin where he was placed on a lounge. Mr. Barr, who knew something of medicine, gave him a calming dose from the submarine's medicine chest, and he became less violent.

"Barton, where did you put that lever?" demanded the ensign.

The man whimpered like a child.