"They discovered us," the girl said. "They have besieged the city ever since the fifty-third year after our landing. They're invisible, of course, but we can see them as openings in the earth. The openings change shape as they move, and of course no natural pit does that. In their own universe, the hollow Earth bounded by its solid atmosphere, they are flying creatures, and their sense of gravity is the reverse of ours." Her clear, fluting voice became steadily duller, losing its inflection as the tale went on. "Before we came here," she said, "we had encountered what our scientists call counter-matter--matter of opposite electrical nature to ours. But this complete inversion of space-matter relationships was unknown to us. The space-beasts knew about it. They are bent on driving us from the Earth...." * * * * * Andreson felt his mind reeling into hysteria again. It was difficult enough to accept the spotless, shining glass chamber and the two winged Varese--but this story of an inside-out universe and its air-treading masters--if only John Kimball had been the one to hear it-- "Sometimes," Atel said reflectively, "I think the Varese have earned their defeat. There was a time when we were carrying the fight into the enemy's own cosmos. But it was their cosmos, not ours, and they knew it very well! Our change of state, while it enabled us to see our foes, could not change our mental orientation. We were lost in that hollow darkness. We could not forget that each great gulf was actually a mountain, the sudden chasms were buildings we ourselves had built,--and the things like tiny burrows which kept opening and closing all about our feet were the footfalls of our brothers. And the space-beasts swooped upon us, each of them with six tiers of wings muttering against the solid magma of the Earth, and our weapons were crude and worthless...." Andreson's mind tasted the concept and rejected it with a shudder. "But surely," he said as steadily as he could, "you must have better weapons, now." "Oh, yes, we have the weapons. But we are decadent, and have lost the initiative to be the aggressors. The machines that accomplished the reversal of state for our ancestors have lain idle for a century in the bowels of our city. We no longer understand them. We are dying, first of all, of old age--the space-beasts are the accident that speeds us along the way. Shall I tell you what we use against them now?" The girl stirred protestingly. Andreson looked at her, but she would not return the glance. Atel went on relentlessly. "Look." From under his tunic he produced a heavy, long metal rod. "A club? But--I don't see how--"