Infernal Affairs by Jordan L. Hawk

Ralgath wants nothing more than to work as a crossroads demon. Too bad he botched his first assignment when a very sexy mortal turned the tables on him. Now he has one chance to get his job back: find two demons who vanished in the human realm. Unfortunately, doing so means teaming up with Chess—the mortal who cost Ralgath his job in the first place.

Chess has spent the last three years using their infernally granted powers to do good. But now Ralgath has a new offer for them: help find the missing demons, and he’ll return Chess’s soul.

After their last encounter, Chess is the last person Ralgath should be interested in. But the passion that initially drew them together still burns hotter than the flames of the Underworld. Chess claims they never meant to hurt Ralgath, but can Ralgath afford to trust them? Because while Ralgath may have Chess’s soul, he’s increasingly certain Chess owns his heart.