Shift by Joel Abernathy

An angel fell and a devil was there to catch him.
My fathers always told me the rules would keep me alive. For Mihail, I’ll break every last one of them.
Never let the blood run cold.
Never let the monster out in the light of day.
Never let a human witness escape.
He saw the secret I keep buried beneath my skin one night so long ago, and I let him get away. I should have killed him, but my soul knows him the way my fangs long to.
He’s got secrets, too. Secrets of the tarnished past. Secrets sharp and rusty enough to ruin us both.
Either he falls or I do.

This is the third book in the Flesh & Bone series. It can be read as a standalone, but it includes characters and references situations from the previous two books.