Merlin: The Mark of Nimueh
A magical plague strikes Camelot and King Uther orders door-to-door searches for evidence of sorcery.

When Gwen’s father (who we’ve never met before) falls sick, Merlin sneaks in to their home after curfew and uses a magical poultice to cure him.

Unfortunately word gets round of the blacksmith’s miracle recovery and Arthur, upon discovering the poultice, can only haul Gwen before his father – who orders her to be burnt as a witch.

Merlin and Gaius then have a race against time to trace the real cause of the plague (contaminated water) to its source and defeat the creature which has appeared in the underground lake that supplies the castle.

The creature, an Afanc, a mythological Welsh water monster, rather resembles the poo demon from Kevin Smith’s Dogma, but combined with all the wandering around in caves, bearing lit torches, that Merlin, Arthur and Morgana do to finally confront it, this makes for a wonderfully evocative Dungeons & Dragons sequence that has helped confirm Merlin as “must see” TV for me.

Ultimately Gaius discovers clues that indicate the beast was summoned by Nimueh (former Bionic Woman Michelle Ryan), an old adversary of Uther, who returns in next week’s episode – The Poisoned Chalice – to seek her revenge on Merlin.

By introducing a recurring villain, Merlin has already upped the stakes and shown – hopefully – that it’s not going to fall into a repetitive, unconnected “monster-of-the-week” routine.