When King Arthur faces a challenge for his crown from the reinvigorated Roman Empire, he must call his supporters from every corner of the British Isles. One of these, Sir Lucan - the Black Wolf of the North - has more reason than most to join the coming campaign. Lucan's beautiful wife, Trelawna, hoping to lead a new, better life in Italy, absconded with a young Roman officer.

Lucan, already a fierce warrior but now with tainted blood due to his battle with the Penharrow Worm, thus turns the mission into a bitter personal vendetta. His former squire, Alaric, soon comes to fear for his overlord's soul, but is more afraid still for the safety of Lady Trelawna, whom he always loved from a distance. Meanwhile, the Roman family Trelawna has fallen in with are the influential Malconi clan, and their matriarchal head is the sorceress Zenobia. She sees it as her motherly duty to stop Lucan with any demonic force she can summon.