Etienne, son of a lord in the kingdom of Armorique, goes to train as a knight with Geraint of Lucanne. Geraint is brave and kind, a good teacher and master - but he has a secret that he has kept from his family. He is bisclavret, a born werewolf. When Geraint is betrayed, Etienne must ally with the local wise-woman and her daughter, themselves bisclavret, to save his lord. But time is running out. If Geraint's enemies have their way, Geraint will soon be trapped in his wolf form.