Repeater One was already in place and ready to operate. Repeaters Three and Four had also been put in position by men from faraway Farside Base. Repeater Two was necessary to bring Farside Base into communication with the rest of the cosmos. Two weeks of lunar night with no word from outside the base and not even Earth to look at in the sky--this would not be good for the men on Farside. McCauley stopped. He'd been moving in that swooping, semi-flying fashion which the lesser lunar gravity allows. He stared at the trail. No, the men had not come back. Yet he'd ordered a party of two to set up the relay unit. It was to be put into place on the very tip of a mountain that was now away below the horizon. There it would be in line of sight of Repeater One, which was relatively near, and Repeater Three, which was farther away but which in turn could relay signals to Four, which was farthest away of all. From Four, the relayed messages would go on to Farside Base. When all this was accomplished, the Grimaldi Base ten miles distant could communicate with Farside through Repeaters One, Two, Three, and Four, and with Earth by line-of-sight transmission; so Farside could communicate with Earth and through Earth Relay with all the other moon bases--in short, with all humanity. But Two should have been up and in operation by now. McCauley shook his head impatiently inside his space helmet. He'd been away from his command for thirty hours, during which he'd traveled twenty miles on foot, at moon gait, to Gerritson Bay. It wasn't a bay, of course, but an intrusion of now-frozen lava into the mountainous country here at the edge of the moon's earthside surface. He'd been met by a moon jeep and had traveled seven hundred miles over a _mare_--one of the dark areas that were once thought to be seas but actually were dry and level--to the main lunar base near Hipparchus. He'd had a one-hour conference with the base commander there, trying to work out something to prevent the first murder on Earth's big satellite. The conference was unsatisfactory. He'd come back to Gerritson Bay and now he'd covered ten of the twenty remaining miles to Grimaldi Base. When he reached Grimaldi the excessively irritating problem of a murder in the making was still unsolved, and now in addition there was the failure to complete placing the relay at the site of Repeater Two. The sledge ought to be in its place on the peak which was invisible from here, and the men who'd set it up should have returned. They hadn't. He flipped on his space radio and said curtly: "McCauley calling relay placing party. Come in!"