"Cecilia" (Keira Knightley) has fallen for "Robbie" (James McCoy) - a man well down the social ladder from her family and their stately home. It's love, though, and the young man is doing his best to fit into their privileged world by studying (at their expense) at Cambridge with a view to becoming a doctor. Meantime, following a scene that she has completely misinterpreted and the reading of a letter that wasn't any of her business, their behaviour is being rather unhealthily scrutinised by her thirteen year old sister "Briony" (Saoirse Ronan) who soon becomes fixated on the couple, on destroy... Lue kokonaan.