Briony is a fictional character from the novel "Atonement" by Ian McEwan. She is introduced as a young girl with a vivid imagination, which leads her to misunderstand events around her. Her actions have significant consequences, particularly regarding her sister, Cecilia, and a family friend, Robbie Turner. As the story unfolds, Briony grows up and grapples with the impact of her childhood decisions. The narrative explores themes of guilt, forgiveness, and the complexity of truth, ultimately highlighting Briony's quest for atonement for her past mistakes.