There's a big cast: Corrupt cops, a hit man, a mafia drug dealer who loves his own product, a psychiatrist who falls for her sociopath patient, and many others. Gould takes the time to give many of them a backstory, but in doing so he doesn't slow down the action. I've never seen the movie made from the book (directed by Gould), but maybe the flashbacks would be a problem there. Here, they're not.
As for the plot, it's another one of those that I can't really describe. There's nothing in it that you'll find unfamiliar, but Gould's way of telling his story is funny, trenchant, goofy all at once. Check it out. As for me, I'm going to read another of his books soon.