In a Dark Ages world drawn from Celtic, British and Roman myth, the Divine Empire's priest Drwc resurrects the demon lord Arawn after a thousand years. The plan is to sacrifice Riannon, priestess of the Gael tribe, and bend Arawn's power toward conquest. Arawn refuses the offering and strikes Drwc down instead. Freed, Riannon takes him as her husband and chief, and Arawn leads the Gael warriors, alongside her brother Arthur and the mage Ogam, against the Empire.