It's homecoming in Absaroka County, but the football and festivities are interrupted when a homeless boy wanders into town. A Mormon "lost boy," Cord Lynear is searching for his missing mother but clues are scarce. Longmire and his companions, feisty deputy Victoria Moretti and longtime friend Henry Standing Bear, embark on a high plains scavenger hunt in hopes of reuniting mother and son. The trail leads them to an interstate polygamy group that's presiding over a stockpile of weapons and harboring a vicious vendetta.