Atonement is set in 1935 and is about 13-year-old fledgling writer Briony Tallis (Saoirse Ronan) and her family who live a life of wealth and privilege in their enormous mansion. On the warmest day of the year, the country estate takes on an unsettling hothouse atmosphere, stoking Briony's vivid imagination. Robbie Turner (Mr. McAvoy), the educated son of the family's housekeeper, carries a torch for Briony's headstrong older sister Cecilia (Ms. Knightley). Cecilia, he hopes, has comparable feelings; all it will take is one spark for this relationship to combust.
