The year is 117. The Roman Empire dominates large areas, but in northern Britain the relentless conquest has stopped because of the elusive, wild and terrifying tribal people known as Picter.
Quintus (Michael Fassbender) is the only survivor of the Picts' brutal attack on a Roman fort, and marches north with the legendary Ninth Legion led by General Virilus (Dominic West). They are ordered to remove the Pictes from the face of the earth and kill their leader. But when the legion is subjected to an ambush on unknown soil, the surviving soldiers in the troop must fight a desperate battle to stay alive behind the enemy line.