Thrown into the alternative universe of 14th-century England, 20th-century mathematician Jim Eckert and his new wife, Angie, have become Sir James, Baron de Bois de Malenconti, and Lady Angela. They are learning how to live and govern in the medieval era, coping as well with the local dragons and other magical manifestations. Suddenly finding himself transformed into a dragon, Jim turns to S. Carolinus, his magician neighbor, who takes him on as an apprentice. When Prince Edward is captured by the French at the Battle of Poitiers, Jim, submitting to feudal pressure, sets out with some companions from his earlier adventures, including the wolf Aargh, to join the English forces. He is chosen for a special mission that involves penetrating the castle of the evil sorcerer Malvinne, councillor to the king of France, where the prince is being held. During ensuing events, Jim finds that he has become chief pawn in a battle with the Dark Powers–with far-ranging consequences.