The Devil's Only Friend by Dan Wells

John Wayne Cleaver is barely an adult, but he's already killed multiple times -- though, as he'd be quick to tell you, he hasn't killed any human beings, despite great urges to do so, only demonic creatures who call themselves the Withered and have lived among mankind for millennia. And, luckily, the authorities have understood this, and recruited him into a special top-secret team to find and eliminate other Withered across the country.

That all sounds good: Cleaver can channel his sociopathic urges towards killing things that really are monsters, and he has allies to help and support him. But those allies don't trust him -- he is still a teenager, and they know he has no normal human empathy -- and one of them, more annoyingly, is a psychiatrist who makes Cleaver sit down for regular sessions and talk through his "issues." (Cleaver can keep going in large part because there are things he just doesn't talk about, and thinks about as little as possible.)

And the leader of the Withered, the one that recruited the others and created the ritual that transformed them, back at the dawn of humanity, now knows about Cleaver. So now there's more than one hunter -- and one of them has been hunting for a very, very long time.

That's where he is at the beginning of The Devil's Only Friend, the fourth novel Cleaver narrates. (See my reviews of the first three for more background.)

The Devil's Only Friend is an excellent contemporary supernatural thriller, but, for me, what really makes this series distinctive is Cleaver's voice. He tells us each of these stories, from deep within his own tormented and deeply non-neurotypical head, and how Cleaver perceives the world and how he keeps himself following his rules and functioning in society is more interesting and important than whether or not he manages to kill any particular demon. (Because this is a series, so we have a sneaking suspicion that Cleaver isn't going to be suddenly killed by a demon on page ten -- but he could lose control of himself, and lose everything he's worked for.)

Only Friend stands alone, or can do so -- it's set some time after the initial trilogy, and isn't as closely linked as those books are. A new reader could start here. I'd recommend going back to the beginning, though -- these are all great books, and why not savor them?