THE RAT MOVED ALONG the rusted steel rail that ran the length of the huge tunnel. To a human being, the tunnel would have seemed to be in utter darkness, but the little eyes of the rat saw its surroundings as faintly luminescent, glowing from the infra-red radiations given out by the internal warmth of cement and steel. The main source came from above, where the heat of the sun and of the energy sources in the buildings on the surface seeped through the roof of the tunnel.
On and on it moved, its little pinkish feet pattering almost silently on the oxidized metal surface of the rail. Its sensitive ears picked up the movements and the squeals of other rats, but it paid them no heed. Several times, it met other rats on the rail, but most of them sensed the alienness of this rat and scuttled
