The Galactic Empire crumbles, and the Foundation, a beacon of civilization, faces its greatest existential threat from within. The Foundation, established by Hari Seldon to shorten a predicted dark age, now finds its carefully laid plans challenged by a mysterious and powerful figure known as the Mule. This individual, possessing uncanny mental abilities, begins to conquer the galaxy, threatening to derail Seldon's psychohistorical predictions and plunge humanity into an even longer period of barbarism. The narrative follows the Foundation's desperate attempts to understand and counter this new force, relying on their scientific knowledge and political maneuvering against an enemy who defies their understanding of the universe.

As the second volume in Asimov's seminal Foundation series, Foundation and Empire is widely regarded as a pivotal work that deepens the exploration of psychohistory and introduces significant new conflicts. Critics often highlight its intricate plotting and the introduction of the Mule as a formidable antagonist who challenges the very foundations of Seldon's predictions. The novel is praised for its intellectual scope, examining the interplay between individual will and historical determinism. Readers frequently commend its ability to expand the universe established in the first book while raising the stakes considerably, making it a crucial and compelling part of the saga.