Sophie receives philosophical questions and chapters of a philosophy course in her mailbox from an unknown sender. She learns about the origins of philosophy while also receiving mysterious postcards addressed to another girl, Hilde. Sophie takes an intensive philosophy course taught by Albert Knox, but strange events occur that seem to blur the lines between reality and fiction. It becomes clear the characters are creations of Hilde's father, known as the Major, with supernatural powers over their world. By the end, Sophie and Albert escape the Major's control and become invisible observers of Hilde and her father, demonstrating how perceptions can change depending on one's philosophical viewpoint.