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.
Sophie Amundsen (Sofie Amundsen in the Norwegian version) is a 14-year-old girl who lives in Norway in the year 1990.
The book begins with Sophie receiving two messages in her mailbox and a postcard addressed to Hilde Møller Knag. Afterwards, she receives a packet of papers, part of a course in philosophy.
Sophie, without the knowledge of her mother, becomes the student of an old philosopher, Alberto Knox. Alberto teaches her about the history of philosophy. She gets a substantive and understandable review from the Pre-Socratics to Jean-Paul Sartre. Along with the philosophy lessons, Sophie and Alberto try to outwit the mysterious Albert Knag, who appears to have God-like powers, which Alberto finds quite troubling.
Sophie and Alberto's entire world is revealed to be a literary construction by Albert Knag as a present for his daughter, Hilde, on her 15th birthday.
As Albert Knag continues to meddle with Sophie's life, Alberto helps her fight back by teaching her everything he knows about philosophy. Alberto manages to find a plan so that he and Sophie can finally escape Albert's imagination. The "trick" is performed on Midsummer's Eve, after Alberto informs Sophie's mother about everything.