An exclamation burst from Darl. A half-inch from the Dome's blazing arc, a hundred yards in actuality, the screen showed a black fleck, moving across the waste! Darl quickly threw in the full-power lens, and the image leaped life-size across the table. The black fleck was the shadow of a space-suited figure that lumbered slowly through the viscous, clinging footing. How came this living form, clad in gleaming silver, out there in that blast-furnace heat? In one of the space suit's claw-like hands a tube flashed greenly. * * * * * Darl's hand shot out to the trigger of the beam-thrower. Aimed by the telescope's adjustment, the ray that could disintegrate a giant space flier utterly flared out at his finger's pressure. Against the lambent brown a spot glowed red where the beam struck. But, warned by some uncanny prescience, the trespasser leaped aside in the instant between Thomas' thought and act. Before Darl could aim and fire again the foe had dodged back and was protected by the curve of the Dome itself. Two white spots showed on either side of Darl's nostrils. His mouth was a thin white slit, his eyes gray marbles. Standing against the wall beside him was a space suit, mirror-surfaced and double-walled against the planet's heat. In a few moments he was encased within it, had snatched a pocket ray-gun from the long rack, and was through the door to the auxiliary air-lock. The air soughed out in response to his swift thrust at a lever, a second door opened, and he was on the outside, reeling from the blast of that inferno of light and heat. For a moment the Earthman was dazzled, despite the smoked quartz eye-pieces in his helmet. Then, as his eyes grew used to the glare, he saw, far below, the erect figure of the stranger. The man was standing still, waiting. His immobility, the calm confidence with which he stood there, was insolently challenging. Darl's rage flared higher at the sight. * * * * * Scorning the ladder that curved along the Dome to the ground, he threw himself at the polished round side of the great hemisphere. With increasing speed he slid downward, the gleaming surface breaking only slightly the velocity of his fall. On Earth this would have been suicidal. Even here, where the pull of gravity was so much less, the feat was insanely reckless. But the heat-softened ground, the strength of his metal suit, brought Darl safely through. He whirled to meet the expected onslaught of the interloper. The green tube was aimed straight at him! The Earthman started to bring his own weapon up when something exploded in his brain. There was a moment of blackness; then he was again clear-minded. But he could not move--not so much as the tiny twist of his wrist that would have brought his own weapon into play.