There was a long silence. Then Birrel said, with just the right lack of conviction, "No, I can't do it." Vannevan stood up. "I think we'd better show him the cavern, Wolt. I don't believe he understands yet just how much the safety of Earth depends on him." Wolt nodded. He rose, too, and walked to the wall. It appeared perfectly blank and solid, but under the pressure of his hand a segment of it swung in, revealing a tiny lift. The three men got in, the door closed, and the lift plunged down. Birrel tried to keep his excitement well hidden. His act was already paying off--apparently they were about to show him something that even the Ruunites didn't know about. Just how he might use that knowledge to help himself and his two friends he could not figure yet. But his stretch in the OSS had taught him well. Keep your mind alert and flexible, play it by ear, and wait for the break which may come in a hundred ways and from the most unexpected sources. The lift let them out onto a narrow platform beside a car that ran from a track through a tunnel hollowed roughly out of bedrock underneath the city. They got into it and the car shot through stale darkness relieved by a few dim lights. It went fast. * * * * * Birrel stole a glance at the other two men, and decided against any precipitate action. Vannevan had something hidden in his hand, and it would be something small and nastily potent as a weapon, he was sure. He'd wait, play it along-- There was light again, sudden and bright. The car burst into it, into vast and unexpected space. For a second Birrel thought they had come back to the surface again. Then he saw the rocky vault high overhead and the walls going away on either side and he knew it was a mammoth cavern. The car stopped. They stepped out onto a platform. "This way," said Wolt. "I want you to see it all." They moved off the platform and onto a railed shelf cut out of the rocky wall. And Birrel stared in amazement. The end of the tunnel and the shelf on which they stood were about halfway up the cavern wall. Below, and stretching away as far as he could see, rank upon rank of great metal shapes stood, some painted in dour red or gray, others naked, gleaming steel or copper. There was no one in the cavern, no sound, no movement--nothing but the brooding silence and the loom of the endless rows of enigmatic mechanisms. Wolt and Vannevan looked down on them, with the faces of men who see a beautiful and splendid vision. And Wolt said, "Do you know what those are?" Birrel said, "No." "And how should you? Your world is still in the nursery. Those are weapons--or they will be, when they are mounted in ships. Mighty weapons, that lack just one thing--the fissionable matter that must power them. The matter that our world doesn't have. Perhaps you understand now why we must raid your atomic stockpiles?"