Quickly Elaine related the story of finding the bomb in the rocks and the peculiar events and our escape which followed. Once, at the mention of the searchlight gun, Professor Arnold raised his hand and coughed back of it. I felt sure that it was to hide an involuntary expression of satisfaction and that it must be he who had sent the gun to Elaine.

He was listening attentively to her, while I stood by the rail, now and then looking out over the water. Far away I noted something moving over the surface, like a rod, followed by a thin wake of foam.

"Look!" I exclaimed, "What's that?"

Elaine turned to me, as Arnold seized his glasses.

"Why, it seems to be moving directly at us," exclaimed Elaine.

"By George, it's the periscope of a submarine," cried Arnold a moment later, lowering his glasses.

He did not hesitate an instant.

"Get the yacht under way," he ordered the captain, who immediately shouted his orders to the rest.

Quickly the engine started and we plowed ahead, that ominous looking periscope following.

In the submarine harbor to which he had been taken, Del Mar found that he had been pretty badly shaken up by the accident to his car. His clothes were torn and his face and body scratched. No bones were broken, however, though the shock had been great. Several of his men were endeavoring to fix him up in the little submarine office, but he was angry, very angry.