In the midst of the largest motorcycle rally in the world, a young biker is run off the road and ends up in critical condition. When Sheriff Walt Longmire and his good friend Henry Standing Bear are called to Hulett, Wyoming, to investigate, things start getting complicated. As competing biker gangs; the Bureau of Alcohol, Tobacco, and Firearms; a military-grade vehicle donated to the tiny local police force; and Lola, the real-life femme fatale and namesake for Henry's '59 Thunderbird come into play, it becomes clear that there is more to get to the bottom of at this year's Sturgis Motorcycle Rally than a bike accident.