Binding Ties — Shannon K. Butcher

They are the Sentinels. Three races descended from ancient guardians of mankind, each possessing unique abilities in their battle to protect humanity against their eternal foes: the Synestryn. Now a warrior must protect his onetime enemy--without succumbing to his darkest desires.

Lyka Phelan is a Slayer, sent to live among her enemy to guarantee lasting peace with the Theronai. Yet she has a secret--and it could make her a slave to their power. But when a pack of Synestryn destroys her home and captures her packmates, Lyka realizes her freedom is a small price to pay for the safety of her people. So she strikes a bargain with the leader of the Theronai--one that reveals her true identity and binds her to him forever.

Joseph thought he knew better than to tangle with the beautiful, hot-blooded Lyka. One misstep could send their races straight back to war. But now he has no choice other than to help her. Forced to protect her with his life, Joseph finds himself increasingly drawn to Lyka. As they risk everything in their fight against the demons, he realizes he must convince her to surrender to him completely--otherwise she will never truly be his.