They found, as they traveled northward and made intermittent landings, that there had been many cities. Now all lay in ruins. There had been great roadways, now covered with the debris of outer space. There had been mighty forests, now miles of petrified black stumps. It was a gloomy sight. In their landings, they had found inscriptions on walls and bas-reliefs carved on mountains. They knew from these what the Plutonians had looked like, and they had a suspicion of what had happened. The Plutonians had been vaguely like men and vaguely like spiders. They had stood upright on four thin, wide-spread legs and had two short arms. Their bodies were wide and squat, and they seemed to have been mammalian and probably warm-blooded. They breathed air out of flat, thin nostrils and their heads joined their bodies without necks. Two oval eyes were set below a jutting bald brow. They had worn clothes, they had driven vehicles, they had flown planes. Their vehicles had globe-shaped power plants. Their airplanes had globes where wings should have been. Their cities and their engines--which existed now only on wall pictures that were probably once advertisements--were built along globe-and-rod principles. "There's no doubt," said Russ, "that the Sun-tapper culture and the Plutonian culture are the same. It's the descendants of the Plutonians that we are fighting." "But how could they have survived?" Burl asked. "This world was never part of the solar system when it was warm." "We'll soon know," said Russ. "Tomorrow we're going to see how far we can get into their polar redoubt. Somehow we've got to blow up that last station." "And I think we three are going to do it," said Haines. "The _Magellan_ will never take the place from the sky. We'll have to do it from the ground." Now they were reminded of Earth again. For the first time since they had departed from the United States, night fell. They had not been on any other planet long enough for such an experience. But the effect here on Pluto was mild. Day was like a bright, moonlight night. Night then meant that the dim Sun had set and, in effect, it merely made the landscape slightly darker. They compared notes late into the night in the rocket plane. By dawn, when again the dim glow shone, they had come to some very definite conclusions about the planet. A number of the drawings on the walls seemed to have some religious significance. They focused on the phases of a moon. There were symbolic representations of this moon, passing through its phases; presumably Plutonian religious and social practices were related to it. "But where is this moon?" Burl had asked.