The armies of Mordred and Arthur begin the Battle of Camlann, where many on both sides are slain. Arthur defeats Mordred and kills him, but Mordred deals Arthur a fatal blow. Sensing his protégé is dying, Merlin leaves Nimue to go to Arthur. Mab's creation seals itself behind him, parting Merlin from Nimue. At the battlefield, Mab's magic is unable to save Mordred, and Arthur lives long enough to tell Merlin to return Excalibur to the place it was found. Merlin gives back the sword to the Lady of the Lake. She tells Merlin she is slowly dying as the Old Ways are rejected and forgotten. Merlin accuses her of lying to him about the guardian of Camelot, but she explains that it was Galahad who was the true guardian and could have averted all this, though she assures Merlin that Arthur's death is not his fault. Merlin encounters Frik among the survivors of Arthur's army, who warns him that although Mab is greatly weakened, she is still dangerous.