Wanted—A party of courageous men, experts in the various trades, to accompany a philanthropic gentleman on a mission of enlightenment to the Middle Ages. Single men only. References exchanged. An opportunity offers to construct anew the history of several benighted nations. If interested, call or write. Percival Tapscott, No. 198 Forty-Third Street.

But the big puzzle: how had he—his earlier self—known that a piece of wire and a bus token would save his life? He had known, all right. Known in advance. But how? And the other five. Probably they were just as precious, or would be.

If you went back to, I would guess, 1946, and worked to prevent your parents’ marriage in 1947, you would still have existed in that year; you would not go out of existence just because you had influenced events. The same would apply even if you had only been in 1946 one microsecond before shooting the man who would otherwise have become your father.

Wanted: Somebody to go back in time with me.
This is not a joke.