As is typical, the book is much better. The leader is unstable. He used to be a DEA agent, but was frustrated that he was unable to arrest so many drug dealers without evidence. He's very frustrated -- a frustration that grows in a very unhealthy manner. The central victim is far from the first that he and his easily manipulated and amoral sidekick abduct. Every rape becomes more horrifying than the last, and very quickly elevate to murder/rapes. Each is more grisly than the last. These guys have become caught up in their own sick pleasures. Any nobility behind the motives have dissipated long ago.

The movie also completely removes Scudder's girlfriend from the story. She is a prostitute and his relationship with her is growing to genuine feelings which, due to her profession, are becoming complicated. (Several books earlier in the series, he did favors for her and she returned the favors in the way she knew best. Their relationship becomes more genuine as well as more convoluted.) It is partially resolved in this book and moves forward significantly. This would be difficult to portray effectively in a movie.

Also, TJ is much more slick and streetwise in the book than he is in the movie. He isn't burdened with the disease.