Father and daughter Aulfric and Sophia have been banished from Avalon and become mortals. If they want to return they must sacrifice Prince Arthur, to the Sidhe Elders.
Sophia (played by Holliday Grainger) was a beautiful young woman who appeared in Camelot with her elderly father, Aulfric. Morgana had a terrifying dream of Arthur dying at Sophia's hands. It emerged that Sophia and Aulfric were Sidhe, magical creatures exiled from the land of eternal life. In order for Sophia to return, she had to sacrifice the soul of a mortal prince to the Sidhe elders. Sophia bewitched Arthur and nearly killed him, but was herself killed by Merlin using her own magical staff.
Aulfric (played by Kenneth Cranham) arrived in Camelot after he and his daughter, Sophia, was rescued from bandits by Arthur. He and Sophia were secretly magical creatures known as Sidhe, but were banished from Avalon (the land of immortal life) because Aulfric killed another Sidhe. He was then forced to live as a mortal but Sophia could return to Avalon if she sacrificed a mortal prince to the Sidhe elders. Merlin prevented them from killing Arthur, and he killed Aulfric and Sophia using Sophia's magical staff.