He heard a colloquy between Kent and Holmes, far away in the lunar mountains. They were evidently climbing somewhere, and part of the climb necessarily took them through deep shadow, where the temperature of the rock was down to night temperature. Their space suits could handle the cold for a certain length of time, but the teeth of one of the men were chattering before he came out into sunlight at the end of the climb. McCauley heard Holmes say sarcastically: "I needed that last pull. Want me to thank you for it?" Kent's voice snapped as he answered Holmes. "I did it solely because McCauley would court-martial me if I came in alone!" A pause, then the remote, transmitted sound of space shoes on stone. Holmes spoke. "There's a way I can kill you easily. All I need do is get myself killed." He laughed without mirth, and Kent said bitterly, "Go ahea--" Then there was silence. The communications officer brought McCauley a message from Lunar Base congratulating Grimaldi Base for completing the communications link between the two hemispheres of the moon. "All right. Forget it," McCauley said. He continued to listen. An hour went by. Then, without warning, there came an explosive "Look out!" There was a crash and then panting. Kent's voice rasped, "Have you gotten killed?" Holmes answered through clenched teeth. "Not yet. But how will I get out of here?" More clankings; more words, painstakingly devoid of solicitude on the one hand, or any amiable emotion such as gratitude on the other. McCauley could visualize exactly what was going on from the words. Holmes had fallen into a pothole, one of innumerable such mantraps scattered at random everywhere. Kent got him out. Holmes grunted to indicate that he could do without more help. That was that. Minutes later, McCauley heard Kent say dourly: "Three hours to Repeater One? We're over three hours now. How's your air?" "All right," Holmes snapped. "When we get to that level place, we'll split the extra tank." McCauley fretted. He could not know how far or how fast the two men were moving, off in that deadly waste of obstacles. Three hours had seemed a fair estimate. But plainly they'd had trouble. Their voices cut off before they reached a spot where they could divide the air in the tank that had to be shared. Then silence, for a long, long time. When McCauley heard any sound again, it was Holmes angrily calling to Kent, demanding that he say whether he needed help or not. And then for a full half hour McCauley listened to the sharp-voiced, sometimes abusive exchanges between the two. Kent had touched the keystone of an unstable rock slope. It gave way under him and went whirling downward in one of those infrequent, slow-motion moon avalanches that are unimaginable until one has seen them. Kent checked himself on the edge of a precipice over which the rolling stones fell in utter silence until after tens of seconds they struck and split, still noiselessly.