Merlyn Britannicus, leader of the colony known as Camulod, is faced with the task of educating his young charge, Arthur, future King of the Britons. Fearing for the life of his nephew when an assassination attempt is thwarted, Merlyn takes Arthur and his boyhood companions Gwin, Ghilleadh, and Bedwyr, to the ruins of a long-abandoned Roman fort far from Camulod. Once there, Merlyn realizes it's time for Arthur to become worthy of the sword he is destined to wield later in his life-the mighty Excalibur.