Patricia Highsmith - The Talented Mr Ripley
Everyone of course knows the movie. Not everyone knows the book. This happens a lot of course. I was in the same situation.
I've now read the book. It's nice. It took me quite a while to get into the book. It seems to start very very slow. But once things start happening, the book is very nice. I ended up really enjoying the book. And eventually, you remember your last impression, not your first impression ;)