Merlin - Season 5 Episode 2

Ruadan rescues his daughter but is fatally wounded in the process. Merlin and Arthur are route-marched to Morgana's wintry hide-out. Mordred shows them some kindness but Merlin, having glimpsed the future, mistrusts him. Merlin and Arthur escape and arrive in the mines below the castle, where they free all the slaves and meet a spirit called the Euchdag, who is herself the Diamar, the "key" which Morgana had been seeking. Mordred saves Arthur from Morgana's attempt to kill him and is rewarded with a knighthood on the return to Camelot. Merlin remains wary despite the Euchdag telling him that Arthur's bane is Arthur himself, not Mordred.