"Sure. Only we can't. Too many guards. It's impossible to get out of this city. I've tried often enough. The only way I managed to survive was by entering the Darkness." His voice trailed away. "That black wall?" "It's a vibration-barrier. None of the Zarno can pass it. It shakes them to pieces--destroys them. The Ancients made it, I suppose, to guard their library." Willard extended his hand in a sweeping gesture. "This is it. All the knowledge of the Ancients--tremendous knowledge--compiled here for reference. If we could only get it out to the world!" Garth remembered something. "Does it mention their power-source?" "Sure. I've had nothing to do for five years but study the library. I could put my finger on the wire-tape recording that explains the process. It's an intricate business, but we could duplicate it on Earth easily enough." Paula would be glad to know that, Garth thought. The secret of the Ancients' power, that could replace oil and coal--a vital secret to Earth now. * * * * * Willard was still talking. "I ran when I heard you coming. I'd been studying one of the recordings, but I thought the Zarno might have got through the barrier somehow.... It doesn't harm humans, luckily, or the robots. I learned a lot in five years." "How did you manage to keep alive?" "I found food. The Ancients had stocked up this place. _Pills!_" Willard grimaced. "They kept me alive, and there was a machine for making water out of the air. But I'm hungry for a steak." Garth scowled. "Doc--one more thing. You know what I mean?" Willard sobered. "I get it, Ed. The cure. Whether or not I--" "Whether or not you've found the cure for the Silver Plague. It hasn't been checked yet. It's still killing thousands on Earth." "So. I wondered a lot about that. Well--the answer is yes, Ed. I know the answer." "The cure?" "Yes. I worked it out, completely, with the aid of the Ancients' library. They were studying it too, but they didn't have quite the right angle. However, they were able to supply the missing data I needed." Willard took from his pocket a small notebook. "I had five years to work on it. So far, of course, it's theoretical, but everything checks. It's the cure, all right." Somehow Garth didn't feel much excitement. Five years ago, he thought, that notebook would have saved Moira's life. Now--well, it would still save life. It would save Earth. But-- He shrugged. "Two good reasons to get back to civilization. The cure, and the secret of the power-source." Willard nodded. "The Ancients died of the Silver Plague, indirectly. They tried to escape by changing their bodies. The library told me that." "Their bodies? How?" "Well--you've seen the robots in Chahnn and here. Originally they were the servants of the Ancients." "Intelligent?"