The dark sorceress Nimueh casts a spell on a dragon egg which she throws into the castle's water supply. The next day, people start dying of a plague which turns their skin white with dark blue veins. Uther believes it to be the work of magic and orders Arthur to search Camelot for the sorcerer. When Gwen's father exhibits symptoms, Gaius warns Merlin a sudden recovery will arouse suspicion, but Merlin cures him with magic anyway. However, when Arthur reports the remarkable recovery, Uther believes Gwen to be the sorceress and sentences her to death. With some prompting from Morgana, Arthur and Merlin set out to defeat the monster and save Gwen.
