Forget minor hazards like nuclear bombs. The discovery of time travel means that everything we know, anyone we know, might not only vanish, but never even have existed.
Against that possibility stand the men and women of the Time Patrol, dedicated to preserving the history they know and protecting the future from fanatics, terrorists, and would-be dictators who would remold the shape of reality to suit their own purposes.
But Manse Everard, the Patrol's finest temporal trouble-shooter, bears a heavy burden. The fabric of history is stained with human blood and suffering which he cannot, must not do anything to alleviate, lest his tampering bring disastrous alterations in future time.