The summer of 1967, in the heart of rural Suffolk, thirteen-year-old Maisie is at her decaying family home, once a medieval abbey. Lucas, a young artist, is painting a portrait of Maisie and her elder sisters - arrogant, beautiful Julia and bookish Finn. In turn, Maisie embarks on a portrait of her own: an account of her family, and of a summer in which the three sisters' lives will irrevocably, and terribly change. Twenty years later it's 1991 in a wintry London. Lucas's now famous portrait of the three Mortland sisters features in a retrospective of his work. Daniel, down on his luck, obsessed by the sisters and determined to understand what happened that last summer at the Abbey, pursues answers to the past.