The evil sorceress Nimueh is back to wreak havoc on Camelot. This time Merlin is her target, and she tricks the young warlock into drinking from a poisoned chalice, causing him to fall dangerously ill.
Arthur must venture to the caves deep beneath the forest of Balor to obtain the antidote, but he does not realise he is walking into a trap. Determined to thwart his quest, Nimueh does everything she can to stop him.
Can Arthur overcome these magical hurdles and make it back in time to save his friend?
BBC One, 7:05pm Saturday 11th October