Bittersweet Magic — Nina Croft

Roz has been indebted to the demon Asmodai for five hundred years, and her freedom is just around the corner. All she has to do is complete one last task for him -- obtain a key that had been hidden in a church centuries ago.

Piers, the Head of the Order and an ancient vampire, is intrigued by the woman who comes to him for help. She's beautiful and seemingly kind, but she's hiding something. And he'll find out who she is and what she really wants once he uses his power to get inside her head. But Piers has no idea that Roz is immune to his mind-control...or that he is simply a pawn in her dangerous mission for freedom.