Edwin Blair, a time-traveler from the 24th Century BCE, has traveled back to the 19th Century to enlist the aid of the Union and Confederate armies at the Battle of Gettysburg to help stop a future pestilence on earth. When he returns to his own time, he has neither memory of how much, if anything, he has accomplished, nor any memory whatsoever of his journey. Suspecting that this might happen during his travels into the past, he has left seemingly insignificant clues that might later help him learn what he has done. When he figures it all out, he realizes that one more journey to the past is necessary and that his problems have just begun. Even worse, he finds out that he needs the help of the very Pests he has been trying to destroy.