John Murdoch wakes in a hotel bathtub with no memory, a dead woman on the floor, and a phone call from a doctor he has never met warning him to run. He is wanted for a series of murders he cannot remember committing. He discovers he has a power he cannot explain — the ability to reshape matter with his mind, a power the city's mysterious rulers call "tuning." And he discovers that at midnight every night, everyone in the city falls asleep simultaneously, the city itself physically reshapes itself, and the inhabitants wake with entirely new memories of lives they never actually lived.
The city has no daylight — it is perpetually night, perpetually noir, perpetually 1940s. There is no outside to the city. The inhabitants do not know this. They have memories of childhoods in places that do not exist, of summers they never experienced, of a world beyond the city that is entirely fabricated. Their entire personal history — the bedrock of their identity — is a construct imposed from outside. And the beings who impose it — the Strangers — are dying, and are trying to understand something about human beings that they cannot grasp: the source of individuality, the thing that makes each person distinctively themselves despite having the same experiences as others.