Using an incantation, Morgause revives the deadly Knights of Medhir and, whilst Merlin and Arthur are the sole survivors of the party sent to beat the knights, Morgause uses Morgana to bewitch Camelot so that everybody except Morgana herself falls asleep, rendering the court defenseless when the knights approach, intent on killing the king. Merlin learns from the Great Dragon that the only way to break the spell is to kill Morgana, so he uses her as his bargaining power to force Morgause to call off the attack. As a consequence he must honour his pledge to free the …
Watch It Here : Merlin Season 2 Episode 12
