"Make a guess, Murgatroyd," said Calhoun. "There are at least a few people in the city who don't want something known to the Med Service. So whatever's the matter, it's not fatal to them. There may be people wandering about like that poor devil we found. Something was fatal to him! Where'd we find more of his type? Since they haven't tried to kill me, we might make friends." Murgatroyd did not answer. He stared absorbedly at a patch of underbrush some fifty yards to the left. * * * * * Calhoun shrugged and started down the hillside. Murgatroyd remained fixed in a pose of intensely curious attention to the patch of brush. Calhoun went on down the farther hillside. His back was toward the brush-thicket. There was a deep-toned, musical twanging sound from the thicket. Calhoun's body jerked violently as an impact sounded. He stumbled and went down, with the shaft of a wooden projectile sticking out of his pack. He lay still. Murgatroyd whimpered. He rushed to where Calhoun lay upon the ground. He danced in agitation, chattering shrilly. He wrung his paws in humanlike distress. He whimpered and chattered together. He tugged at Calhoun. Calhoun made no response. A figure came out of the thicket. It was gaunt and thin, yet its garments had once been of admirable quality. It carried a strange and utterly primitive weapon. It moved toward Calhoun without lightness, but with a dreary resolution. It bent over him and laid a hand to the wooden projectile it had fired into his back. Calhoun moved suddenly. He grappled. The gaunt figure toppled, and he swarmed upon it savagely as it struggled. But it was taken by surprise. Pantings sounded, and Murgatroyd danced in a fever of anxiety. Then Calhoun stood up quickly. He stared down at the emaciated figure which had tried to murder him from ambush. That figure panted horribly, now. "Really," said Calhoun in a professional tone, "as a doctor I'd say that you should be in bed instead of wandering around trying to murder total strangers. When did this trouble begin? I'm going to take your temperature and your pulse. Murgatroyd and I have been hoping to find someone like you. The only other human being I've seen on this planet wasn't able to talk." He swung his shoulder-pack around and impatiently jerked a sharp-pointed stick out of it. It was the missile, which had been stopped by the pack. He brought out his lab kit. With absolute absorption in the task, he prepared to make a swift check of his would-be murderer's state of health. It was not good. There was already marked emaciation. The desperately panting young woman's eyes were deep-sunk: hollow. She gasped and gasped. Still gasping, she lapsed into unconsciousness. "Here," said Calhoun curtly, "you enter the picture, Murgatroyd! This is the sort of thing you're designed to handle!" He set to work briskly. But presently he said over his shoulder: