On the hottest day of the summer of 1935, thirteen-year-old Briony Tallis sees her sister Cecilia strip off her clothes and plunge into the fountain in the garden of their country house. Watching her is Robbie Turner, son of the Tallis's cleaning lady, whose education has been subsidized by Cecilia's and Briony's father, and who, like Cecilia, has recently come down from Cambridge. By day's end, their lives will be changed – irrevocably. Robbie and Cecilia will have crossed a boundary they had not imagined at its start. And Briony will have witnessed mysteries, seen an unspeakable word, and committed a crime for which she will spend the rest of her life trying to atone...