It Walks Among Men — A.R. Williams

Gerhardt is hired to kill a priest, but his instincts tell him there is more to the job than he's being told. He questions the man who hired him and discovers that the priest he's sent to kill isn't human at all--but a demon.

Undeterred, Gerhardt accepts the job. When he arrives at the cathedral, he realizes he knows the target. Somehow, Gerhardt's past and future are connected to this mysterious priest, one in which his bloodline plays an important role in the war between gods, dragons, and men.