Two months before, Kenneth Torrance had returned to the whaling submarine _Narwhal_, of which he was first torpooner, with a confused story of men who were half-seals that lived in mounds under the Arctic ice,[1] who had captured him and--he found--had also captured the second torpooner, Chanley Beddoes. In breaking free from their mound-prison, Beddoes had killed one of the sealmen and had been himself slain minutes later by a killer whale, one of the fierce scavengers of the sea which the sealmen trapped for food even as the _Narwhal_ sought them for oil. Ken Torrance alone came back. [Footnote 1: See the February, 1932, issue of Astounding Stories.] Over their doubts, he had stuck to his story. Later, he had repeated it to officials of the Alaska Whaling Company, who worked the submarine and several surface ships. They in return had sent him to a private sanitarium in the State of Washington for a rest which they hoped would "iron out the kink" in his brain. Here Ken had been for six weeks, while the exploring submarine _Peary_ nosed her way northward toward the Pole. Here he had been, all unknowing, while the world hummed with reports of the _Peary's_ disappearance in that far-off ever-shrouded sea of mystery. She might, Ken knew, have struck a shaft of underwater ice, sending her to the bottom; some of her machinery might have cracked up, paralyzing her; the ice-fields under which she cruised might have shifted suddenly, crushing her ribs--of these perils the world knew as well as he. But the submarine's crew was prepared for them; the _Peary_ was equipped with a circular saw for cutting up through the ice from beneath, and she carried sea-suits which would allow her men, if she were wrecked on the bottom, to leave her and get up on the ice and wait for the first searching plane. Why, then, had not the planes which scoured the region found the survivors? That was the mystery--but not to Ken Torrance. There was another peril, of which he alone knew. Not far from where the _Peary's_ last radio report had come, a group of hollowed-out mounds lay on the sea-floor, swarming with brown-skinned, quick-swimming creatures. Sealmen, they were--men who, like the seals, had gone back to the sea. Months ago, Second Torpooner Chanley Beddoes had killed one of them. They were intelligent; they could remember; they were capable of hate and fear; they would be desirous of leveling the debt! There, Ken felt sure, lay the reason for the _Peary's_ baffling silence, for the non-appearance of her men. There might still be time. No one of course would listen to him and believe, so he would have to go in search of the _Peary_ and her crew himself. Standing by the window, Kenneth Torrance quickly planned the several steps which would take him to the Arctic and its silent ice-coated sea.