All through the long Martian day Shelby paced the length of his tether, pausing occasionally to look out of the window and to think. By nightfall he was in a state bordering upon complete dejection. Not that he was weak; Shelby could face trying situations shoulder to shoulder with the stubbornest and cleverest men that Earth or Mars could produce. But he was human and had his limitations. Recapture after a glowing promise of freedom and safety for his people, his love, and himself had almost crushed him. Only half interestedly he wondered when Hekalu Selba would strike. He knew that it would be very soon. In vain he tried to tell himself that he had no real proof of the Martian's power, but always a vision of those black horrors swooping down like living thunderbolts upon Taboor or New York or Chicago made him realize how futile would be any resistance that the planets could offer. Even if there were but fifteen hundred Space Men, and Shelby was certain as actual knowledge that there were many more, and even if they must fight with their bare hands, still they would be a formidable menace. Within an hour's time they could strike in a dozen different places on the surface of a planet. Shelby did not know that already there were forces of Fate in action which neither he nor Hekalu Selba himself had been able to foresee--forces however, which boded no good for the worlds. Koo Faya brought the Earthman his noonday and evening meal. With each came a note from Hekalu, both exactly alike: "Remember the Atomic Ray." Doubtless the Martian sought by endless repetition of this message to undermine his captive's nerves to a point where he would divulge the secret. At dusk there was the sound of activity aboard the _Selba_--muffled shouts and the drone of generators being tuned up. Then the slow rocking and swaying of the vessel which told that her levitator plates were in action, raising her off the ground, through the atmosphere and out into the void. Shelby looked out of the window, saw that the stars were growing brighter and the sky blacker. A searchlight was playing from somewhere on the ship, for in the shadow of the planet it was very dark. The beams swung back and forth stabbing through the swarms of Space Men who flew in a cluster about the _Selba_. The lights lingered for several instants on the forms of four great metal cubes that were being lifted up through the gaseous envelope of Mars by a number of the larger discs the Earthman had seen resting beside them in the valley that day. Shelby threw himself upon his bunk. He gave one quick glance at the blob of darkness on the other bunk at the farther end of the room, wondered vaguely who or what the creature could be, and then, mentally and physically exhausted, went quickly to sleep. * * * * *