A huge monster, the Questing Beast, is on the loose near Camelot. Morgana has a nightmare of Arthur's death, but he ignores her warning and is bitten by the creature before Merlin slays it. The Great Dragon tells Merlin that in order to save Arthur he must travel to the Isle of the Blessed, where he meets Nimueh. She gives him the antidote (water from the Cup of Life) but warns him another life must be sacrificed to save Arthur's. Merlin gives the antidote to Arthur and the prince recovers, but Merlin's mother arrives in Camelot with a terrible illness. Merlin prepares to return to the Isle of the Blessed, however Gaius gets there first. As Gaius sacrifices himself, Merlin faces the greatest test so far of his emotions and his magic powers in a final showdown with Nimueh.