Demon 

by Tosca Lee

 

From "Malcolm's Review of Demon" at goodreads
Clay's wife recently left him for another man, his writing career is stalled, his personal life is a mess, and he's falling behind in his work as an acquisitions editor at a small Boston publisher. He desperately needs a break, an infusion of something positive into his life that will cast out the worst of his past while giving him a goal he can believe in.

 
See the full text of Malcolm R. Campbell's review of Demon at goodreads.com