In his last moments, King Arthur, mortally wounded by his son Mordred, reveals to Sir Bedivere that he has another son and that it will be the knight's job to protect him. In addition, the dying king asks his friend to take Excalibur back to the lake to keep her safe. Years later, fate puts Bedivere and Owain, Arthur's lost son, face to face. They will have to work together to regain the throne, usurped by Mordred, and will count on Merlin and Excalibur to fight.