Merlin - Season 1 Episode 3

The dark sorceress Nimueh casts a spell on a dragon egg she throws into the castle's water. The next day a plague causes people to die, their skin turning white with dark blue veins. When King Uther orders Prince Arthur to search all Camelot for the sorcerer he believes to have caused the epidemic, only a magic trick saves Merlin from having his book found. When Gwen's father exhibits symptoms, Merlin waves Gaius's warning by curing him. Arthur reports the recovery, and Uther orders her execution at the stake. Merlin tells Gwen's caring mistress, Morgana, only Arthur can help him fight the monster (an afanc), which they search for in the dragon's cave.