The Tears of Uther Pendragon - Part 1 (S03E01)

Merlin and Arthur have been on many quests in search of the missing Lady Morgana. The despondent Prince is all but ready to give up. But as they recover from their latest skirmish, a bruised, bloodied figure emerges from the mist... it is the Lady Morgana. King Uther is overjoyed, but then starts to lose his mind. Merlin thinks that magic is the cause; could this be the work of his dutiful ward? The young warlock puts himself in grave danger trying to find out whose side Morgana is really on. (BBC)