"First we must find out where you are going. And when."

Professor Coypu staggered across the laboratory, and I followed, in almost as bad shape. He was mumbling over the accordion sheets of the computer printout that were chuntering and pouring out of the machine and piling up on the flow.

"Must be accurate, very accurate," he said. "We have been running a time probe backward. Following the traces of these disturbances. We have found the particular planet. Now we must zero in on the time. If you arrive too late, they may have already finished their job. Too early and you might die of old age before the fiends are even born."

"Sounds charming. What is the planet?"

"Strange name. Or rather names. It is called Dirt or Earth or something like that. Supposed to be the legendary home of all mankind."

"Another one? I never heard of it."

"No reason you should. Blown up in an atomic war ages ago. Here it is. You have to be pushed backward thirty-two thousand five hundred and ninety-eight years. We can't guarantee anything better than a plus or minus three months at that distance."

"I don't think I'll notice. What year will that be?"

"Well before our present calendar began. It is, I believe, A. D. 1975 by the primitive records of the aborigines of the time."

"Not so aboriginal if they're fiddling with time travel."

"Probably not them at all. Chances are the people you are looking for are just operating in that period."

"How do I find them?"