In 2nd century Roman Britain, the Roman Ninth Legion under General Virilus is ordered to march north and wipe out the Picts, fierce Celtic tribes threatening the northern frontier. Centurion Quintus Dias, the sole survivor of a Pictish raid on a Roman outpost, is rescued and joins the legion. With the help of a Pict scout, Etain, who harbors deep animosity towards the Romans, the legion ventures deep into hostile territory. However, they are ambushed, Virilus is captured, and the legion is decimated in a brutal assault. Surviving members, including Dias, find themselves stranded behind enemy lines, fighting for their lives while being pursued by Pict warriors seeking revenge.

Dias leads the few remaining soldiers through treacherous terrain, evading Pict forces and struggling against the harsh elements. As they navigate the perilous landscape, internal conflicts and dwindling supplies add to their challenges, forcing them to make desperate decisions to survive. Their journey is one of sheer endurance and relentless pursuit, testing their resolve and camaraderie. The remaining soldiers strive to return to Roman territory, but their path is fraught with danger, deception, and betrayal, pushing them to the limits of their strength and honor.