Something flashed across his field of vision. Regan caught only a glimpse of it, then reasoned that it must have been a bridge, spanning the enclosed river. He twisted himself around to a prone position and tried to think constructively. Somewhere there had to be an exit to this land. For his sake, there had to be, although of course this guaranteed nothing. But surely these people made use of this abundant supply of water. It would be fresh and good to drink after its long passage through the Earth, despite its source in the salt ocean. They would use it for irrigation, probably, and perhaps somewhere it was channeled for transportation--of a more comfortable kind than his own. And they might use it for power. Certainly its rushing strength would be tapped. This thought scared him. He pictured a giant hydroelectric plant into which he would be swept and in the bowels of which his body would be mangled by the blades of a turbine. He had to slow his mad passage. He maneuvered the equipment attached to his spacesuit and pointed the rocket exhaust ahead of him. He flicked on the power and felt his speed being cut. The powerful current pressed from behind him like a live thing, but the rocket thrust was strong, too. His progress slackened to the pace of a canoe. Balancing himself behind the makeshift braking apparatus was difficult, both because the torrent threatened constantly to turn him end for end, and because his strength was only a memory of itself. But somehow Regan managed to achieve an equilibrium which allowed him to look about and reassure himself that the city was still there. Its position had shifted on the horizon to a point slightly behind him, but there apparently was no end to the expanse of this underground world. The road was there, too, still parallel to the roofed-over river. A surge of hope went through him as he spotted a man walking along the road. Regan braked himself still further, until his speed matched that of the man. The man's costume was a brief one--knee-length trousers, a vestlike garment over a white skin, and sandals--so apparently the climate was tropical. Regan stared hard at the man, mutely begging him to turn. Both Regan's hands gripped the rocket tube; he didn't dare let go to wave. Then, as though he had been reached telepathically, the man looked in Regan's direction. Regan couldn't make out his expression, but apparently it was one of disbelief. The man stopped, took an indecisive step and then ran toward the river. He jogged alongside it and now Regan could see his face clearly. * * * * * It was an intelligent face--round, broad-nosed, the eyes almond-shaped and the hair abundant and black. The man's body was stocky and powerful, graceful as he ran beside the tubed-in river. He waved and smiled, and Regan hoped his own answering smile was visible behind the faceplate of his spacesuit.