Whilst out on a routine hunting trip, Arthur and his men encounter a huge and terrifying monster - the Questing Beast. Uther ignores Gaius` warning, that the creature`s bite is always fatal, and sends Arthur and his knights out to kill it. The beast knocks Arthur unconscious and bites his shoulder. As Arthur`s life hangs in the balance, Merlin must travel to the Isle of the Blessed and there strike a potentially fatal bargain with the sorceress, Nimueh. The young warlock is the only one who can save Arthur - but at what cost?