The Sloppy Joe was on the valley floor now, and ahead the bubble covering the city was drawing closer. The sun was almost gone; lights were appearing inside the plastic shielding. Born and raised on Mars, Tom had seen the teeming cities of Earth only once in his life ... but to him none of the splendors of the Earth cities could match the simple, quiet beauty of this Martian outpost settlement. There had been a time when people had said that Sun Lake City could never be built, that it could never survive if it were, but with each successive year it grew larger and stronger, the headquarters city for the planet that had become the new frontier of Earth. The radiophone buzzed, and the airlock guard hailed him when he returned the signal. Tom gave his routine ID. He guided the tractor into the lock, waited until pressure and atmosphere rose to normal, and then leaped out of the cab. Five minutes later he was walking across the lobby of the Interplanetary Council building, stepping into the down elevator. Three flights below he stepped out into the office corridor of the U.N. Interplanetary Council on Mars. If there was trouble, this was where he would find it. He paused for a minute before the gray plastic door marked MAJOR FRANK BRIARTON in raised stainless steel letters. Then he pushed open the door and walked into the ante-room. It was empty. Suddenly he felt a touch on his shoulder. Behind him, a familiar voice said, "Hello, Twin." * * * * * At first glance they looked like carbon copies of each other, although they were no more identical than identical twins ever are. Greg stood a good two inches taller than Tom. His shoulders were broad, and there was a small gray scar over one eye that stood out in contrast to the healthy tanned color of his face. Tom was of slighter build, and wirier, his skin much more pale. But they had the same dark hair, the same gray eyes, the same square, stubborn line to the jaw. They looked at each other for a moment without speaking. Then Greg grinned and clapped his brother on the shoulder. "So you got here, finally," he said. "I was beginning to think I'd have to go out on the desert and find you." "Oh, I got here, all right," Tom said. "I see you did too." "Yes," Greg said heavily. "Can't argue with the major, you know." "But what does he want?" "How should I know? All he said was to get down here fast. And now he isn't even here himself." "Is Dad on Mars?" Tom asked. Greg looked at him. "I don't know." "We could check the register." "I already checked it. He has not logged in, but that doesn't mean anything." "I suppose not," Tom said glumly. They were silent for a moment. Then Greg said, "Look, what are you worried about? Nothing could have happened to Dad. He's been mining the Belt for years." "I know. I just wish he were here, that's all. If he's in some kind of trouble...." "What kind of trouble? You're looking for spooks."