Mr. Monster

I killed a demon. I don't know if it was really, technically a demon, but I do know that it was some kind of monster, with fangs and claws and the whole bit, and he killed a lot of people. So I killed him. I think it was the right thing to do. At least the killing stopped.
Well, it stopped for a while.

In I Am Not a Serial Killer, John Wayne Cleaver saved his town from a murderer even more appalling than the serial killers he obsessively studies, using his own repressed homicidal proclivities to even the odds.

But it turns out even demons have friends, and the disappearance of one has brought another to Clayton County. Soon there are new victims for John to work on at the mortuary, and a new mystery to solve. But this time something's different. John has tasted death, and the dark nature he used as a weapon—the terrifying persona he calls "Mr. Monster"—might now be using him.

No one in Clayton is safe unless John can vanquish two nightmarish adversaries: the unknown demon he must hunt, and the inner demon he can never escape.