After a flash-forward preamble that sees protagonist Quintus Dias (played by Michael Fassbender) stumbling half-naked through the snow, it's established that action

unfolds in 117 A.D., on the very edge of the Roman Empire, in what's now Scotland. Like many a superpower that would follow in Rome's footsteps, the would-be continental conquerors are finding it hard work vanquishing the local barbarian horde, in this instance the Picts. Using guerrilla tactics, these fierce warriors bedevil the Roman legions with constant raids on the Romans' forts, one of which wipes out Quintus' cohort.

Quintus is taken prisoner instead of slain. A skirmish with the Roman Army's Ninth Legion liberates Quintus, who joins forces with his countrymen, led by roistering Gen. Titus Virilus (Dominic West).

To help them find the Picts' leader, Gorlacon (Ulrich Thomsen), the Ninth are using mute Pict woman Etain (Olga Kurylenko). But she turns out to be a double agent who leads the Ninth into a trap, resulting in the near-total slaughter of the legion and Virilus' capture.

Only Quintus and a handful of men survive, including sturdy Bothos (David Morrissey); cheeky Thax (J.J. Feild); middle-aged Brick (Liam Cunningham), who was, naturally, just about to retire; fleet-footed African Macros (Noel Clarke); killer-shot Greek Leonidas (Dimitri Leonidas); and cook Tarak (Riz Ahmed), from the Hindu Kush. From this point on, plot adheres to a standard chase/horror-movie template as the Romans are picked off by the Pict hunters. Thankfully, Marshall is inventive when it comes to killing characters, deploying just about every weapon in the ancient-world arsenal as well as wolves. Only a few stopoffs for bantering and back-story revelations, and an interlude at the home of an ostracized Pict woman (Imogen Poots) provide breathers from the relentless, sharply cut action sequences.