Wrapt in Crystal by Sharon Shinn

On a planet of barren beauty, two religions—as different as sun and shadow, joy and grief—are bound together by death….

A serial killer is stalking the priestesses of both sects—and Interfed Agent Cowen Drake must immerse himself in an unfamiliar world of stark spirituality to catch the killer. A world that will trap him between opulence and sacrifice, between desire and duty, and between two extraordinary women—one who could become the killer’s ultimate victim.