A mischievous girl accuses her older sister's lover of a crime he did not commit, only to find that her words have irrevocably and permanently changed the lives of all involved in a film that re-teams the filmmakers behind Pride & Prejudice
to adapt the best-selling 2002 novel by author Ian McEwan
. The year is 1935, and as the summer heat takes hold, 13-year-old fledgling writer Briony Tallis watches her older sister, Cecilia (Keira Knightley
), get undressed and go frolicking in the garden fountain on her family's country estate. The housekeeper's son, Robbie (James McAvoy
), a childhood friend and recent Cambridge graduate, also witnesses the innocent act. When Robbie and Cecilia subsequently cross a particularly sensitive boundary and the scheming Briony accuses Robbie of an unspeakable transgression for which the boy is wholly innocent, the repercussions of her unfounded claim threaten to affect all three for decades to come.