Walt Longmire is back after the escapades of First Frost and encounters one of his most baffling cases in Wyoming's brutal and unforgiving Red Desert. When Blair McGowan, the mail person with the longest postal route in the country of over three hundred mile a day, goes missing the question becomes--where do you look for her? The Postal Inspector for the State of Wyoming elicits Sheriff Longmire to mount an investigation into her disappearance and Walt does everything but mail it in; posing as a letter-carrier himself, the good sheriff follows her trail and finds himself enveloped in the intrigue of an otherworldly cult. Packed to the brim with twists and turns, the 21st novel in the New York Times bestselling Longmire series pushes Walt to his absolute limits, forcing him to wrestle with the impossible question: What good are your morals, if you're marked for the dead letter office?