Sophie's World: A Novel About the History of Philosophy

One day fourteen-year-old Sophie Amundsen comes home to find two notes in her mail asking, "Who are you?" and "Where does the world come from?" which lead her to ponder the great questions of Western philosophy.
Before she knows it, she is enrolled in a correspondence course, covering Socrates to Sartre and beyond, with a mysterious philosopher. But Sophie is receiving a separate batch of equally unusual letters. Who is Hilde? And why does her mail keep turning up in Sophie's world?
To unravel this riddle, Sophie must make use of the philosophy she is learning. But the truth is far more complicated than she could have imagined...