特种女兵布伦纳·贝克和伴侣迪伦在亚拉巴马州的荒山野林里徒步旅行,误入黑帮毒贩的老巢。迪伦被残忍杀害,布伦纳有幸逃生。这群残暴的毒贩没有想到的是,布伦纳作为美国陆军第75游骑兵部队的第一中尉,誓让他们所有人血债血偿。While camping deep in the backwoods of Alabama a married couple, Dillon and Brenner Baker are out hiking when they stumble across an illegal drug and gun storage compound. Before they can flee the area the Cartel captures and tortures them. The Cartel makes two mistakes though, they kill Dillon and think they killed Brenner. Now, 1st Lieutenant Brenner Baker of the Army's 75th Ranger Division is on a one woman killing mission carving up everyone in her path until there's only one person standing, her. Brenner is, an Army of One.