Sheriff Walt Longmire is enjoying a beer when a younger sheriff shows him a photograph of twenty-five armed men standing in front of a Challenger steam locomotive. It transports him back to a time when, fresh from the battlefields of Vietnam, then-deputy Longmire accompanied his boss, Lucian Connolly, to the annual Wyoming sheriff's junket held on the excursion train known as the Western Star. Armed with his trusty Colt .45 and a paperback of Agatha Christie's Murder on the Orient Express, the young Walt was ill-prepared for the machinations of twenty-four veteran sheriffs, let alone the cavalcade of curious characters that accompanied them. Now the photograph—along with an upcoming parole hearing for one of the most dangerous men Walt has encountered—hurtles the sheriff into a head-on collision of past and present, placing those he loves most squarely on the tracks of runaway revenge.