Hekalu started, and then making a hurried gesture to Alkebar which indicated that he was to guard the inventor of the Atomic Ray, he drew his automatic and dashed down the corridor to investigate the disturbance. The Earthman however, was in no mood to be guarded. No longer shackled, he leaped to his feet and over to the center of the room. The great voiceless beast from the stars stood before the doorway with his long arms outstretched. He was not trying to capture the Earthman--only seeking to block his path. But Shelby had no time to waste. Gathering himself together, he hurtled straight for the ankles of his opponent. The fact that the artificial gravity of the ship was of the same strength as that of Mars--only a trifle more than one-third that of Earth--added to the effectiveness of his plunge. The mighty-muscled Alkebar, puzzled by the unheard-of tactics of his agile though vastly weaker foe, suddenly found himself in a sprawling heap on the floor. Shelby leaped over him through the door, slammed it, and raced precipitately down the corridor. In the meantime Hekalu Selba had reached Janice Darell's room, but when he had unlocked it and had thrust his head inside to see what the matter was, a heavy urn, deftly aimed, had crashed full into his face. Shelby saw him sprawling in the passage badly dazed, and a split second later Jan dashed from her cabin. She looked around, and when she saw Shelby coming swiftly toward her she flashed him a quick smile of triumph. But Alkebar had wrenched the portal of the Earthman's recent prison open, and was in hot pursuit. He was tugging frantically at the pistol in his belt. "Run, Jan, quick!--To the control room!" Austin shouted. He caught up Hekki's automatic which had dropped from the Martian's grasp when he had fallen, and wheeling, fired at the black colossus. The bullet struck Alkebar's right hand with which he was raising his pistol. The tough natural armor which covered the monster from head to foot prevented it from doing any serious damage, but it must have stung badly, for his weapon clattered to the floor. While he was stooping to recover it, Shelby hurried forward to catch up with Jan. It was but a few yards to the control room. If they could get there, overcome whoever was in charge and barricade themselves in, they could master the ship!