His reason hinted temptingly that the voice he had heard might well not have been that of his son. How many voices were there in all creation that were precise echoes of each other? Thousands? Millions, even. But among them, there was of course the _one_. And he must know. He had to know. The Contraption. Again, what had it done? It had transmitted himself and Dot into their physical counterparts on a parallel time-track. If the blue glow of the contraption had touched Terry and Mike, then they too would have been transmitted. But because they had not appeared in the cellar when the transmission was complete, he and Dot had assumed that they had been just outside the Contraption's limited range. That was it, of course--the cellar. That was what had thrown them off, confused their logic. Through some quirk of coincidence, the other Blair, Senior Quadrate Blair and his wife had been in their cellar at the time of the switch. Had they been anywhere else--anywhere else at all, even just upstairs, the mistake in logic would not have been made. And if Madame Blair had no sons, Terry and Mike would not have been transmitted at all. But Quadrate and Madame Blair had had sons. Two, ten years old. He remembered when Tayne had told him of their transfer from his quadrant to Tayne's own.... Ordered by Gundar Tayne, Director. He remembered. He remembered how thankful he had been that they had not been his. But now--now, fantastically, they were. Because when the switch happened, Ronal and Kurt Blair had not been in the cellar. They had been on Venus. But it was too much, the coincidences--the marriage of two counterparts; their children, same sex, same age. And then he remembered what he had told Grayson so terribly long ago. _There's a million possible results when you go fooling around with the structure of the universe, Carl_ ... * * * * * Thousands of voices in the universe that were exact echoes of each other. But Terry and Mike were here, and there was no doubting that. And in Tayne's quadrate, the one beside which he was even now marching. Oh, he was doing well with his thinking! He had narrowed the field down to a trifling two hundred fifty thousand! And he knew that by any direct means that would not arouse Tayne's too-willing suspicion, it was as far down as he would narrow it.