Quintus Dias (Michael Fassbender) is a centurion, and the sole survivor of a raid conducted by the Picts against his Roman frontier fort. He is captured by the Picts, but later escapes and is found by the Ninth Legion and its commander General Titus Flavius Virilus (Dominic West). General Virilus has a mute scout named Etain (Olga Kurylenko) who secretly detests the Romans and ends up betraying them to Gorlacon (Ulrich Thomsen) the Pictish king. Now Quintus Dias, along with the few others who survive the betrayal, must try to escape pursuit by Etain and her group of Pictish warriors and return to Roman territory. Fear, flight, and betrayal are the name of the game as they make their way home.