It was the sound of engines under them! Ignoring Larry now, Von Ullrich staggered to the conning-tower hatch. It was battened fast. Frantically he beat on it. This much Larry saw, as he knelt there getting his breath. Then he rose, took Diane by the arm and led her down. And he was none too soon, for with a lunge the U-boat got under way. But she seemed unable to lift her loot-laden mass from the ocean floor, and headed off crazily across the plateau, dragging her keel in the sand. With fascinated horror, they watched the craft's erratic course, as it swung loggily westward and headed toward that yawning abysm from which they had all so lately risen. The last sight they had of the U-boat was as it reached the brink, its despairing commander still standing in the conning-tower, hammering vainly on that fast-bound hatch; then they turned away faint, as the doomed craft plunged down, stern up, into those crushing depths. * * * * * Professor Stevens now joined them. "A lesson in avarice," he said gravely, when he had greeted his daughter with heartfelt relief. "And a typical fate of fortune hunters! Let that be a lesson to you, young man." "Amen!" said Larry. "But what happened, my dear?" asked the professor of Diane, a moment later. "Why were they in such a hurry to be off?" "Because the sensible Antillians seized their opportunity and overcame their guards, while we were below," was her reply. "When we got back, we found the pyramids flooded, so there was nothing else for them to do but go." So that was the explanation of those gathering, furtive hosts in the lower level, thought Larry. Now he knew what they had been waiting for! They had been waiting for that usurping vandal to depart. And how they must be gloating now, down there! "But why were they so eager to abandon the _Nereid_?" asked the savant, still puzzled. "It it a better boat than theirs, even if I do say so myself." "Because I put it out of commission, directly we got back up here," replied Diane. "But not permanently!" she added, with what Larry knew was a smile, though he couldn't see her face, of course, through the helmet of her pressure-suit. "Little thoroughbred!" he exclaimed, half to himself. "What did you say, Mr. Hunter?--Larry, I mean," she inquired. "N--nothing," he replied uneasily. "Fibber!" said Diane. "I heard you the first time!" "Just wait till I get out of this darned suit!" said Larry. "I guess I can wait that long!" she told him. And if Professor Stevens heard any of this, it went in one ear and out the other, for he was thinking what a report he would have to make to his confrères when they got home--particularly with half a boatload of assorted idols for proof. [Illustration: He pressed the tiny switch in the flame-tool's handle just as Arlok came through the door.] The Gate to Xoran _By Hal K. Wells_ A strange man of metal comes to Earth on a dreadful mission.