"Miss Graham," interrupted Rocky impatiently, "there is nothing at all amusing about the job we are engaged in. It is, moreover, no work in which a girl should be involved. You would oblige me by returning to the Fort on the first transport bus--" "Oh, no! This is a Patrol roller, and I requisitioned it in my own name. Either I drive it or--" Stubbornly--"or it doesn't roll!" "Very well, then. You may take us as far as the desert path. But there we leave you. And now, let's get going. We have wasted enough time as it is." Rocky motioned Bud into the roller. A few seconds later they were speeding noiselessly out on the highway toward the spot where Rocky had seen the truck leave the road. * * * * * Russell had been keeping an eye on his chronometer for the past little while, estimating the number of daylight minutes left to him. On this little satellite there was no such thing as dusk or twilight. At ninety million miles from Sol, there was little enough sunlight. Titan's main radiance came not from the Sun, but from its own parent planet which, a huge, shining platter in the sky, gathered up and reflected to its tiny satellite the thin illumination from afar ... for all the world like a gigantic, reflecting mirror. Titan revolved on its axis in fifteen hours, twenty-three minutes. Almost the whole of its day period had elapsed now. Shortly.... Yes, even as he studied out the problem, night came suddenly and completely to this part of Titan. It descended instantaneously, snuffing out the light as a finger presses the wick of a candle. Only the stars remained, glowing white in the rich, jet vastness of outer space. The girl reached toward the dashboard instinctively, but Rocky's hand clasped about her wrist. "No! Don't!" "But--but I was only going to turn on the lights." "I know. But you mustn't. We're getting very close to the spot now. Can you see to drive without them?" "Why, I--I guess so," said Lynn dubiously. She was surprised, herself, to learn that she could. "Why, yes! The road stands out like a dark ribbon against the sands on either side. Isn't that strange?" "Not so strange at that," grunted Rocky. "I'm beginning to get an idea about the mysterious T-radiation of this planet. I may be completely wrong, of course, but so far my theory fits all the facts I've observed. There's something I would like to know, though. Grossman told us the soil killed humans. I wonder _how_ they die?" "I can answer that. Daddy told me the first day I was here. He was warning me against ever leaving the shielded areas ... the Fort, the city, the roads. He said that if they wander onto the soil of Titan without protection, humans just shrivel up and crumble into dust like--like mummies!"