I had heard so much about Sophie's World, that the actual reading disappointed me. A story within a story is how it started off, with chunks of Philosophy 101 course for dummies interspersed within the story. But as the philosophical exploration reached 20th century, things went haywire and I had a distinct feeling that the author didn't know how to end it.
It failed to excite me either as a novel or as an introduction to Philosophy. The story starts of with Sophie getting letters addressed to another girl called Hilde. She tries to find more about this mystery and a strange philosophy teacher Alberto Knag enters the picture. He starts explaining to her the story of philosophy from pre Socratic days. Sophie and Alberto find that they are characters in a story written by a Major with UN to his daughter Hilde. This twist makes the story interesting for some time, as the characters try to escape the author. However, the story goes crazy from the time the Major comes back home.
As an introduction to philosophy, the book is just about ok. Sartre gets more space than Nietzche, Buddha is the only Asian philosopher who is mentioned in passing, and the book messes up the Indian Caste System. Too many such irrirtants.
If you need a short course on introduction to Philosophy, read Will Durant's Story of Philosophy. Not that I remember anything of what I read, but I do remember that book gave me a distinct feeling of ephemeral sense of achievement when I finished reading as against a vague irritation at the end of Sophie's World.