During the Hundred Years' War, Europe was further torn by the Breton Wars of Succession, a schism that made an unlikely heroine of Joanna of Flanders, Countess de Montfort and Duchess of Brittany. With her husband in prison, Joanna's rightful place was in Brittany as regent of the duchy for their five-year-old son and heir, John of Brittany, but she took up arms and led troops into battle. Famed for the defense of Hennebont in 1342, Joanna unexpectedly disappeared and did not reappear in public. What happened to her, and why? Solving a medieval mystery, Julia Sarpy traces Joanna's fate to a castle in Yorkshire, where the valiant aristocrat was held under orders of England's Edward III.