Dark Heat by Leigh Wyndfield

Caelan has a secret, one she can’t reveal to anyone, even her King. When she’s thrown into the dungeon, she understands just what an easy life she’d led as the healer for the court. To save herself, she strikes a bargain with Garron, a warrior whose only desire is revenge. Their special powers unite, turning lust into something unforeseen. Soon they are forced to choose between freedom and what’s growing between them.