I read this about 10 years ago, when I was 16 and still a little bit of a Christian. It frightened me enough that I had to sleep with the lights on for a few weeks, but I still loved it, especially the battles between angels and demons and the demonic possession. Another reviewer described this as "Christian fantasy," and I agree with that. I'd love to read another (better?) novel about angels, demons, and Christian mythology in general, so if anyone reading this knows of one that's good, please let me know! :)