Born Of Night. Number 1 in series

Command Assassin Nykyrian Quiakides once turned his back on the League - and has been hunted by them ever since. Though many have tried, none can kill him or stop him from completing his current mission: to protect Kiara Zamir, a woman whose father's political alliance has made her a target. As her world becomes even deadlier, Kiara must entrust her life to the same kind of beast who once killed her mother and left her for dead.
Old enemies and new threaten them both and the only way they can survive is to overcome their suspicions and learn to trust in the very ones who threaten them the most: each other.