A town called Why / by Rick Lenz.

Colleagues of Frank Gaines, a half-Apache, Arizona desert town police detective, know him as a courageous man. Gaines doubts it; he suspects he's afraid of not behaving courageously. He goes into therapy. It creates a new problem: he is falling in love with his therapist, a striking, full-blooded Apache woman, Sunny Kacheenay, granddaughter of a great shaman, with mystical gifts of her own. A distant maternal relative of Gaines dies by shotgun blast. Against her own best professional instinct, Sunny is forced to tell Gaines that by ancient, ancestral law, his sacred duty is to find, torture and kill the murderer. Jokingly, Gaines tells her it's not the 1800s anymore. Sunny doesn't laugh. In the process of trying to hunt down the most malignant villain Gaines has ever heard of, he begins to test his courage for real and to recognize his true feelings about life, love, and courage.--Publisher.