This long, dense novel, a bestseller in the author's native Norway, offers a summary history of philosophy embedded in a philosophical mystery disguised as a children's book-but only sophisticated young adults would be remotely interested. Sophie Amundsen is about to turn 15 when she receives a letter from one Alberto Knox, a philosopher who undertakes to educate her in his craft. Sections in which we read the text of Knox's lessons to Sophie about the pre-Socratics, Plato and St. Augustine alternate with those in which we find out about Sophie's life with her well-meaning mother. Soon, though, Sophie begins receiving other, stranger missives addressed to one Hilde Moller Knag from her absent father, Albert. As Alberto Knox's lessons approach this century, he and Sophie come to suspect that they are merely characters in a novel written by Albert for his daughter. Teacher and pupil hatch a plot to understand and possibly escape from their situation; and from there, matters get only weirder. Norwegian philosophy professor Gaarder's notion of making a history of philosophy accessible is a good one. Unfortunately, it's occasionally undermined by the dry language he uses to describe the works of various thinkers and by an idiosyncratic bias that gives one paragraph to Nietzsche but dozens to Sartre, breezing right by Wittgenstein and the most influential philosophy of this century, logical positivism. Many readers, regardless of their age, may be tempted to skip over the lessons, which aren't well integrated with the more interesting and unusual metafictional story line.