One day Sophie comes home from school to find two questions in her "Who are you?" and "Where does the world come from?"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...