Sophie's World is a 1991 novel by Jorstein Gaarder about a teenage girl named Sophie learning about the history of philosophy from a mysterious middle-aged man. After receiving mysterious messages in her mailbox, Sophie begins a correspondence with the 53-year-old philosopher Alberto Knox, learning everything from Plato to Sartre. Eventually Sophie's story is revealed to be a story written by Albert Knag for his daughter Hilde. The plots intertwine, Hilde struggles to free them and finally Sophie and Alberto escape the narrative control of Albert.