"I'm scared of letting all these people down. Like the whole human race. At least if I get blown up as well, they can say I died heroically. Assuming I ever existed at all." When Bernice Summerfield visits the People—an incredibly advanced civilisation living in a Dyson Sphere—she discovers that even in utopia, they still have their problems. An illegal time travel experiment threatens a war which could destroy them all. Rather than risk it, the People and their ultra-powerful computer, God, are prepared to eradicate the source of the problem—the ancient city of Babylon. But such action would involve the death of a quarter of a million human beings, and do incalculable damage to Earth's history. Babylon—and the human race—have one hope. Benny returns to the cradle of civilisation to try and stop the interference. She has just one week to prevent a catastrophe that could mean she will never be born. Her only assistance comes from a Victorian linguist who has stumbled across the experiment himself. But he's no help at all—even though he has a power neither of them suspects.