Dashed ashore from a violent storm, Casca finds himself in Scotland which is riven by a succession crisis. The old king is dead and two rivals vie for power. The English king, Edward Longshanks, chooses one and then insists on running Scotland through his puppet choice.

The Scots object and Casca is drawn in the resulting war, joining forces with Scottish rebel William Wallace and fighting with him against the forces that England send in to enforce their rule.

With help from a Scottish warrior Angus, Casca finds a place to stay and falls for Angus's sister Kathleen, who willingly becomes the Eternal Mercenary's lover.

But when the war turns against the outnumbered Scots, Casca becomes hunted and has to not only fight to remain free, but also to save Kathleen from a gruesome fate at the hands of the English.