Well, this is not really a question of identifying a book. But it is interesting, so I’m going to share it anyway.
A mystery keyword searcher asked:

Can Christians write about vampire or werewolf books?

I am not a Christian, so forgive me if I’m misinterpreting things, but the answer seems pretty simple. Of course they can. The traditional vampire, with his allergy to the cross, seems ready-made for the Christian horror writer. And werewolves, who often have a conflict between animal nature and human morality, seem like they’d work out just fine as well. Demons, witches, all kinds of supernatural creatures, and even the end of days appear in the Bible– it seems to me that it is simply the framework the writer uses that makes the difference.

Horror is traditionally conservative– evil is usually defeated, at least temporarily. That’s not to say that all horror has a moral, or that evil is defeated in all of horror fiction, because it’s certainly true that horror, especially today, can deal with impersonal evil, or can even be amoral– a good story, but not necessarily with a definite stance on right or wrong. But horror as a genre does give writers an opportunity to address faith, and questions of faith. I think this very thought-provoking blog post by horror author Maurice Broaddus, is worth reading if you are interested in this topic. There are people who think that it’s not possible (or at least extremely difficult) for Christians to write horror, and there’s an interesting discussion of that here. I’d say that whether what’s marketed as “Christian horror” really falls under the umbrella of the horror genre (which I would argue has some pretty broad boundaries, based on the kinds of books we are solicited to review here) is a different thing, than whether horror can be written by Christians (which is addressed in depth in this blog post over at TheoFantastique). Personally, I don’t care whether a book in any genre is written by a Christian, pagan, atheist, etcetera, so long as it does the job for me without hammering me over the head with a message.

At any rate, the question at hand is whether Christians can write about vampires and werewolves, not whether Christian horror is truly horror. I really think the answer to the original question is “yes.” As Mr. Broaddus says “If God could communicate through a burning bush and a donkey, surely He could communicate through a few scary stories.” Very aptly put.

Editor’s note:  A 2020 update! I’m adding another link here regarding this topic that I just learned of thanks to Mike Duke.