Commonwealth is a novel by Ann Patchett that follows two families, the Keatings and the Cousins, over five decades after an affair between the parents, Beverly and Bert, at a christening party unites them in an unconventional family structure. The story explores the lasting impact of this event on the six children, who form a deep bond while spending summers together, and how their shared history becomes the basis for a famous author's bestselling book, forcing them to confront their past and the ownership of their own stories.