Merlin - Season 1 Episode 13

The Questing Beast is on the loose near Camelot, and Arthur, ignoring a warning from Morgana who has dreamed that it will kill him, is bitten by the creature before Merlin slays it. Arthur sinks into a coma and the Great Dragon tells Merlin he can only save him by traveling to the Isle of the Blessed. On arrival there Merlin meets the witch Nimueh, who gives him the antidote, water from the Cup of Life, but warns him that, to save Arthur's life, another must be sacrificed. Arthur drinks the water and recovers but Merlin discovers the witch was not lying – his mother is consequently endangered. This will lead to the greatest ever test of both his emotions and his magic powers as he returns for a last show-down with Nimueh.