In which we find out that Kilroy really was there.
When I was very, very young—about the time I thought up the idea of writing a story in which all of humanity is killed off except a man named Adam and a woman named Eve—I thought it would be nice to write a series of stories in which many of the mysteries of human history are explained by time travelers. (I even wrote one, in which the American Revolution is started by a time traveler sent back to fire the Shot Heard Round the World.) It does not say much for a story by Asimov that it has the same kind of plot.
Of course, living over fifty years after “Kilroy Was Here” is a fad, the story seems kind of pointless, too. It would be like somebody from the 2030’s reading a story in which smiley faces are shown to be aliens from another planet. Who would care? So it is with this story. A modern audience finds no real satisfaction from finding out how the “Kilroy Was Here” thing got started.