On the hottest day of the summer of 1935, thirteen-year-old Briony Tallis sees her sister Cecilia plunge naked into the fountain in the garden of their country house. Watching her too is Robbie Turner who, like Cecilia, has recently come down from Cambridge. By the end of that day, the lives of all three will have been changed for ever. Robbie and Cecilia will have crossed a boundary they had not even imagined at its start. Briony will have witnessed mysteries, and committed a crime for which she will spend the rest of her life trying to atone.