Having seen the movie the book didn't have me guessing at all, since the movie was very true to the book.
If I hadn't seen the movie I'm sure I would have been as clueless as I was when I watched the movie! I'm usually pretty good at figuring things out, but not this time, and I loved that!
I do agree that the ending sort of makes the rest of the book (or movie) not making much sense, but to be honest, I don't care! Loved it anyway!