On the hottest day of summer in 1934, Briony Tallis sees her older sister Cecilia strip off and plunge into the fountain in the garden of their country house. Watching her is her childhood friend, Robbie Turner. By the end of that day, the lives of all three will have changed forever: Robbie and Cecilia will have crossed an unimagined boundary, and Briony will have committed a crime for which she will spend the rest of her life trying to atone.