When Morgana kidnaps Gwen and locks her in the top of a fairytale tower, it’s up to Merlin, Arthur and his Knights to save her.

This is a nasty, dark tale with Morgana using gooey mandrake roots to wage psychological warfare against Gwen, tormenting her with visions of her own fears and insecurities before offering kindness. By the end of the episode, in a surprising twist, we learn that Morgana was successful in brainwashing Gwen, who is now working with Morgana to bring down Arthur.

This isn’t an episode for young kids. The scares here are far more unsettling than in the earlier ghost-Uther episode. The screaming in the Dark Tower of the title is creepy enough, but when you add the Knight’s trek through the graveyard surrounding the tower and a shocking death, you’re left with little ‘uns who won’t go to bed. That said, the creepier content of this episode makes it all the better for older viewers. Considering it’s a show about magic, it’s surprising that it’s taken Merlin this long to do what is essentially a horror episode (mixed with a bunch of princess-in-the-tower fairytale nods).

This is a gorgeous-looking episode, from the vine-entangled Impenetrable Forest (they like their literal names in Camelot) to the almost desert-like surroundings of the tower. The Knights and their red cloaks are always a godsend to cinematographers but this episode gets some particularly striking visuals out of them. This episode also manages to do a Knight vs. Enchanted Sword fight that actually works on screen and makes for a genuinely exciting, tense action sequence. Merlin has come a long way in the special effects department since it began (although those snakes at the beginning didn’t look particularly convincing).

Of course, the big shock of this episode was that we lost a Knight. Sir Elyan fell at the (unseen) hand of a magic sword after rescuing his sister. It’s a shame – Adetomiwa Edun often didn’t have much to do, but when he did he excelled. He was probably the best actor of the Knights, and I’d have rather lost Leon or Percival (God knows he’s only there for his arms) before Elyan, but I guess his death was needed to push Gwen that last little way towards Morgana’s side. Still, it’s hard not to feel uncomfortable when a show kills off their only black Knight.

There were some great performances this episode, particularly from Angel Coulby, who always impresses when she’s given something to do. She sold the baby steps of Stockholm Syndrome very well to kids who may struggle to understand what Morgana was trying to do to Gwen. It was also nice to see Merlin step up and take the lead when Arthur’s emotional involvement in the quest compromises him. I’d have liked to see a little bit more of Arthur being dangerously reckless in the search for his beloved – instead, Elyan took that role.

With Mordred and now Gwen bringing danger to Camelot, the showrunners are clearly trying to shake up the Morgana-does-something-evil format, which was desperately needed. Hopefully this episode has set up an interesting new dynamic for the series – at least until Gwen is de-enchanted, anyway.