I found this in a used book store - I had seen the movies "The Exorcist" and "The Exorcist II: Heretic" but had not yet seen the third movie. It was clear reading this that it was meant to be a direct sequel to the book, and the second movie was something created by producers and not the author (which is probably why it sucked). I was confused and didn't really enjoy the story, which follows the police detective from the first book as he tries to figure out murders similar ones committed by a now-dead serial killer. There just didn't seem to be enough of a link to the first book.