Everything bad happens because of three characters wanting money that shouldn't be theirs. Of course, without them doing the questionable act of taking the money, there'd be no novel: a short story, maybe, but not this novel. I once didn't know that a lot of drama comes, or at least starts, from characters doing the wrong thing. I know that now.
I announce now that I will never kill for money. I'm sure you were worried.
(By the way, years later this refuses to stop being funny to me: My sister-in-law Cindy hated the film version and said "It should be called A Stupid Plan! I mean, what was the point of the movie: 'Don't trust Gary Cole'?")