As the cave filled with a whirring tumult Darl had a chance to examine the Mercurian natives crowding around his prostrate body. They were little yellow midgets, ranging from eighteen inches to two feet in height. Half of their small stature was taken up by snouted heads, with saucer-like, crimson eyes, and long white tusks jutting from foam-flecked mouths. The trunks were globular. The spindling legs and thin arms ended in sharp claws. There was an impression of animal ferocity about these tiny beings that stamped them as utter savages. His captor was speaking to the Earthman again, his horny beak parted in what might have been a grim smile. "My friends remind me that I promised you to them. They have not forgotten how you and your fellows drove them from their burrows." Darl was suddenly cold, though the sweat still streamed from his bound body. An uncontrollable shudder took him as he saw what the diminutive claws of the midgets held. While the Dome was still an unfinished framework one of the Terrestrian artisans had somehow been isolated from his fellows. Thomas had been of the party that found what was left of him, and the memory was still a throbbing nightmare. "Once more! Will you give me the recognition signal?" Darl shook his head, and prayed for sudden death. The Martian spoke to the dwarfs. They started forward, saliva drooling from their tusks. Darl gritted his teeth. He would hold out as long as was humanly possible. A shrill rhythmic whistle came from somewhere outside. The blue giant started and snapped something to the Mercurians. Then he turned to Darl. "I must leave you for a little while," he said. "You have till I return to change your mind." With a parting admonition to the savages he was gone through a side door that Thomas had not noticed before. * * * * * Grateful for the postponement, however short, of the inescapable ordeal, Darl took stock of his situation. He lay, firmly bound, on the gritty rock floor of a low-ceiled cave about twelve feet square. In one wall was a door of red metal. The portal through which the Martian had vanished was next to it. Darl repressed an exclamation when he saw the opposite wall. It was of solid metal, bluishly iridescent. That was beryllium steel, the alloy from which the barriers at the terminals of the surta mine were fashioned. He forced his head higher. There were the marks of the jointures, the weldings that he himself had made. The discovery seemed only to emphasize the helplessness of his predicament. His faithful Venusians, Ran-los, Ta-ira, and the rest were just on the other side of the three-inch plate of toughened steel. Three inches--yet it might have been as many hundred miles for all the help they could give him.