Guardian of the Night (Harlequin Nocturne Series #137)

The Guardian. An immortal with incredible strength, created centuries ago to protect the purity of the vampire bloodline and fight those who would abuse its power. As one of the seven Blood Knights, Mason LanVal spent lifetimes honoring his vows without wavering. That all changed the night he found Faith.

Faith James will do anything to save her missing sister. Even if it means risking her own life. She sought Mason for help. Instead she found more questions, and the key to unlocking her own latent Lycanism. She is a woman and a trueborn Lycan, so her pull on Mason is twice damned. Yet he can't tear himself away.

With just one kiss, the blood gift Mason gives Faith sets in motion an all-consuming desire that is forbidden to indulge, but impossible to ignore….