One day fourteen-year-old Sophie Amundsen comes home from school to find in her mailbox two notes, each with a question: "Who are you?" and "Where does the world come from?" From this irresistible beginning, Sophie becomes obsessed with questions that take her far beyond what she knows of her Norwegian village. Through successive letters, she enrolls in a kind of correspondence course, covering Socrates to Sartre, with a mysterious philosopher, while also receiving letters addressed to another girl. Who is Hilde? And why does her mail keep turning up? To unravel this riddle, Sophie must use the philosophy she is learning--but the truth turns out to be far more complicated than she could have imagined.