Who's the demon in Angels in Demons?

The answer to that question is: Ron Howard. I just got back from seeing Angels and Demons, which in my opinion is a phenomenal book, it is NOT however a phenomenal movie. I have not been as disappointed in a movie since I saw The Lost World. What are the rules with taking liberties with another artist's work? What does Dan Brown think about it? I mean there are HUGE fundamental building blocks of the story that are not even mentioned in the movie. I need to do some research on the worst film adaptations for great books. If I find something good I'll post it here. Has anyone out there seen it and read it? Let me know! Oh wait, no one reads this blog..nevermind

David