Merlin: Season 1, Episode 13

1 - 13: Le Morte d'Arthur

When out on a hunt, Arthur encounters a huge monstrous creature never before seen. Gaius realises it is a Questing Beast, a creature conjured from the nightmares of a long-dead king, whose bite is always fatal. When Arthur faces the creature again, it is vanquished, but he is bitten and his life hangs in the balance. Merlin is told by the Great Dragon to seek the Isle of the Blessed, where members of the old religion have the power to save the future king. However, upon his arrival, he finds that there is a price to pay.