Jim stood still, listening. There was no sound from beyond that door. The silence was a vast womb about them, menacing. Jim slid the door noiselessly open; they stepped inside and stared around. They saw huge circling tiers of peculiarly constructed dynamos. They were in operation, Jim knew that, for he could feel a certain surge of power even though there was no sound. A bewildering network of cables led from the dynamos to a central, predominating machine that towered fan-like above them all. It was this electronic tower, he knew, that created the swirling pillars of strength that surged upward and outward to support the vast cavern roof overhead. Then they saw Bhruulo. He was in a little glassite room at the foot of the electronic tower. Tiny wheels and dials were banked around him, and he was busy making delicate adjustments. So busy that he didn't see them standing just inside the door. Now Jim heard the insistent voice of the Dim-Ing in his mind again: "Kill him! Do it at once! Do as you promised...." Jim didn't need the prompting voice, but he wasn't going to ray a man down from behind; besides, he doubted if his beam would penetrate that glassite cage. He stepped quickly to one of the dynamo stanchions, and drew Kaarji down beside him. He waited, despite the Dim-Ing's impatience that he could feel seething within him. Bhruulo finished his adjustments at last, and stepped out of the cage. He was still a good fifty feet from Jim. He turned, to go deeper into the maze of machinery. Jim arose and said quietly: "Bhruulo!" The aged Martian whirled with amazing agility. Jim saw the look of incredulity that leaped into his eyes. Bhruulo leaned heavily forward, his two hands gnarling about his cane. Then his lips quirked into a toothless smile, and he started to say something. That was to throw Jim off guard. Simultaneous with his speech he lifted his hands lightning-like, and the cane levelled. But Jim was expecting that. With a single sinuous movement his pistol was in his hand, its bluish beam was pencilling out. It caught Bhruulo squarely in the chest before he could press the button on his own weapon. He staggered forward, his cane-weapon sagged; he tried to level it again but could not. Still he staggered forward, hatred mingled with horror in his eyes. With amazing strength his spindly legs carried him across the room, as he mouthed unintelligible Martian words. [Illustration: The electronic beam caught Bhruulo squarely in his chest.] Jim fell back a step. He hoped Bhruulo would not find strength in his arms. Would that damned Martian never die? Jim knew his beam had bored a hole clear through the creature's chest; he could see the blackish blood oozing from it. Jim felt a cold horror gnawing at the pit of his stomach even as he aimed carefully and the electro-beam flashed out three more times. He saw three more holes rake across the Martian's chest.