American Demon (The Hollows #14)

What happens after you've saved the world? Well, if you're Rachel Mariana Morgan, witch-born demon, you quickly discover that something might have gone just a little bit wrong. That the very same acts you and your friends took to forge new powers may have released something bound by the old. With a rash of zombies, some strange new murders, and an exceedingly mysterious new demon in town, it will take everything Rachel has to counter this new threat to the world--and it may demand the sacrifice of what she holds most dear.