In 1935, Briony Tallis is a 13-year-old girl from a wealthy English family and has just finished writing a play. Briony attempts to stage the play with her three visiting cousins, twin boys and their teenage sister, Lola; however, they get bored and decide to go swimming. Briony stays behind and witnesses a significant moment of sexual tension between her older sister, Cecilia, and Robbie Turner, a servant's son (a man that Briony has a childish infatuation with). Robbie returns home and writes several drafts of letters to Cecilia, including one that is explicitly sexual and erotically charged. Initially written for the sake of humour, he does not intend to send it and sets it aside. On his way to join the Tallis family for dinner, Robbie asks Briony to deliver his letter, only to later realise that he has mistakenly given her the prurient draft. Briony secretly reads the letter and is simultaneously disgusted and jealous. She tells Lola of its contents and they call Robbie a âsex maniacâ while debating whether to turn him in to the police. That afternoon, Lola and her younger brothers meet a friend of the Tallis family, a wealthy chocolate manufacturer named Paul Marshall. Though he is much older than she, he excites Lola by flirting with her and treating her like an adult.That evening, Cecilia confronts Robbie about the letter which she has since read. They meet in the library where they make love and tenderly confess their love for one another. During the act, Briony watches through the partially open door and her confused emotions about Robbie become heightened. At dinner it is revealed that Lola's twin brothers have run away; a search party is sent out and Briony goes off alone into the woods looking for them. She eventually stumbles upon a man running away from apparently raping Lola. Lola claims that she does not know the identity of her attacker, but then claims it was Robbie after Briony suggests that it must have been the âsex maniacâ who attacked her. In a fit of pique, the still-hurt Briony tells everyone (including the police) that she saw Robbie commit the act. She shows Robbie's shocking letter to her mother and the police. Everyone believes Briony's story except for Cecilia and Robbie's mother; Robbie is arrested and sent to prison.Four years later, Robbie is released from prison on condition that he join the army. He is assigned to A Company, 1st Battalion, Royal Sussex Regiment and sent to France, where he is separated from his unit and attempts to return to them at Dunkirk on foot. He is then shown reuniting with Cecilia (who has not spoken with her family since the incident) in London six months earlier, where they renew their love before he is shipped off to the French front. Briony, now 18, has joined Cecilia's old nursing corps at St. Thomas's in London because she wants to be of some practical use to society after giving up an offer she received from Cambridge. Her attempts at contacting her sister go unanswered as Cecilia cannot forgive her for Robbie's unjust imprisonment. Robbie, gravely ill and wounded, finally arrives at the beaches of Dunkirk where he waits to be evacuated.Sometime later, Brionyâat last fully understanding the consequences of her false accusationâvisits the now-married Cecilia and Robbie to apologise to them directly. However, her apologies are rather weak and ineffectual; Cecilia coldly replies that she will never forgive her, while Robbie, in a rage that almost becomes physical, confronts Briony and demands that she immediately tell her family and the authorities the truth. Briony admits she knew soon after the incident that the real rapist was Paul Marshall, but that Lola cannot testify against him in a court of law because they have recently been married.Decades later, an elderly Briony (now a successful author) gives an interview about her latest book, a autobiographical "novel" called âAtonement.â She reveals that she is dying of vascular dementia and states that this last book is one she has been working on for most of her adult life. Briony confesses that the book's ending (in which she apologises to a married Cecilia and Robbie) is fictional: Cecilia and Robbie were never married and never saw each other again once he left for war. In reality, Robbie died at Dunkirk of septicemia while awaiting evacuation and Cecilia died a few months later as one of the flood victims in the Balham tube station bombing during The Blitz. Briony hopes that by reuniting them in fiction she can give them the happy ending they always deserved. The last scene of the movie shows a happy Cecilia and Robbie together once again in what could either be afterlife or a figment of Briony's imagination.
Output: Question: What is Briony dying of?, Answer: vascular dementia.