Sophie begins receiving enigmatic, anonymous letters addressed to herself, as well as letters directed to Hilde, whom Sophie does not know, from Hilde's father, shortly before her fifteenth birthday. They cause her to start thinking about the "big questions" - who are you, why are you here, etc., and eventually lead her into an unusual relationship with a mysterious older gentleman who becomes something of a mentor.
I did learn more from this book about philosophy than I knew before, which was a pitifully negligible amount; perhaps a straightforward philosophy textbook would have suited me better. The "story" vehicle, in my opinion, ranged from stiff, jerky, contrived, and stilted, to downright chaotic and maddening. I kept plugging away at it, hoping to find what had prompted the good reviews I'd seen, but I never did. The most valuable lesson I took away from it was to never again waste time reading a book I can't stand.