Cornwall, England, 1193. Eleanor of Aquitaine, the indomitable dowager queen, has ordered all of England onto a war footing while her son King Richard languishes in a German dungeon. Gwendolyn de Cardinham, the defiant wife of an absent crusader, protects and defends her estate, Penhallam, with her sword and the garrison of men that she commands. While travelling to deliver a captured mercenary of would-be usurper Prince John to a nearby gaol, her constable takes her on a detour to the local prior, who gravely informs her that King Arthur's mythical sword, Caliburn, is destined to be hers. When Gwendolyn discovers that Prince John has been hunting for Caliburn, she realizes she is in a unique position to end the wayward prince's rebellion. Determined to protect Penhallam and its tenants at any cost, Gwendolyn travels to London to present herself to the dowager queen, placing herself in the middle of the brothers' duel for the throne. But Gwendolyn has kept a secret from even her constable that could put all of Penhallam-and herself-at risk if the queen discovers it.