Why is Robbie in disgrace?

Robbie Turner is in disgrace because of the lie of an upper-class child named Briony Tallis. She witnesses Robbie, the lower-class son of a maid, flirting with her sister, Cecilia. Briony, only thirteen years old, misinterprets Robbie's actions, as he and Cecilia, long friends, are now in love with each other. When Briony sees her cousin Lola being attacked by an assailant, Briony thinks that Robbie is Lola's attacker and accuses him. As a lower-class person, Robbie has few rights in the justice system, and he is sent to prison. Briony later reveals to the reader that she lied about having seen Robbie attacking Lola (and that it was actually a sexual encounter) and that the real attacker was someone else—a man who wound up later marrying Lola. However, Briony is not able to reveal the truth in his lifetime, and Robbie dies in the war in a state of disgrace.