Sex, Lie and Vampires ~ Katie MacAlister

This is the third book in the Dark Ones series. In this novel, Nell, a Medieval history professor and charmer, has been hired to find Damien, a Dark One child, who has been abducted and is being held by a demon lord. Along the way, she meets Adrian, a dark one known as Adrian the Betrayer, as he is bound to a demon lord, and had turned Dark Ones over to him in the past.