Briony starts out the novel as a 13-year-old who witnesses adult behavior she does not yet understand and judges Robbie to be a "maniac." It is her false testimony that dooms Cecilia and Robbie's future. She ends up going into nursing during World War II to bury her guilt in hard work, and finally becomes a celebrated novelist. On the occasion of her 77th birthday party, Briony admits that she fabricated a happy ending for Cecilia and Robbie; they actually both died in the war. She has been diagnosed with dementia and will not live to see her novel published.
Despite having a college education (but no degree), Cecilia is rather aimless in her goals for the future and sticks around her home. After several strange encounters with Robbie, her childhood friend and son of the Tallis family's charlady, she realizes that she is in love with him, and he with her. She is distraught when Briony falsely accuses him of Lola's rape, and she is Robbie's only supporter besides his mother, Grace Turner. Cecilia goes on to become a nurse, seeing Robbie only once more before being killed during the London Blitz. She never forgives Briony for her crime against Robbie and her.
Robbie is a studious young man, and Jack Tallis sees so much potential in him that he agrees to pay for his education to become a doctor. After seeing Cecilia undress and jump into the fountain, Robbie realizes he is in love with her and writes her a letter to apologize for his behavior. He makes several mistakes: sealing the obscene version of the letter in the envelope, using Briony as his messenger, not finding a more private place to make love to Cecilia, and going out on his own to search for the Quincey twins when they run away. These mistakes lead to his being accused of raping Lola. He is sentenced to prison on the basis of Briony's testimony and then sent off to fight in World War II (1939–1945), where he dies of infection from shrapnel wounds.
Like her mother, Hermione Quincey, Lola is conniving and used to getting her way. Although she only 15 years old, she attracts the attention of the much older Paul Marshall, who attacks and rapes her. Despite his violence, however, Lola fancies herself in love with him, and is relieved to have Robbie as a convenient scapegoat for Paul's crime. She allows an eager Briony to speak for her. Later, she marries Paul and becomes Lady Marshall—a socialite and philanthropist.
Paul is a charming and pleasant young man who is used to being able to do what he pleases because of his social status. He invents Amo chocolate, a cheap candy bar with no cocoa in it, and becomes even richer by profiting from the war. Although Paul is the actual villain of the novel, he suffers no consequences, even in Briony's fictional version.
Emily is a long-suffering, upper-class wife stricken with migraine headaches. Grudgingly, she takes in her sister Hermione Quincey's children over the summer, and this leads to Lola being raped on her watch. Even though she "knows everything" about what happens in her house, she willfully turns a blind eye to the truth and goes along with Briony's accusation of Robbie Turner—partly because it's convenient, and partly to get back at her absent husband via his protégé, Robbie.