Abyss - The Prometheus Project, #4

At the beginning of the 22nd century, humanity has survived a challenge to its survival and has commenced the task of rebuilding. An elite corps of fallen angels called the Watchful Host remains in the earthly realm to help-but someone is hunting them. Once the angel Turiel, Tupperman chose to remain in this realm after his mission was completed in order to aid the Watchful Host. When he is framed as a killer of his fellow fallen angels, Tupperman knows not only that he will be sacrificed next, but that it's time for his final quest.
His only clue is a stone, which leads him to New Mexico-and a woman who enchants him completely. Tupperman never counted on finding love, nor that his mission would include a challenge from a dark force and known cheat. Can he save Kara and complete his quest, or will taking Lucifer's wager cost him the woman who has claimed his heart?