An atmospheric pre-credit sequence set the tone for a tense episode chock full of jumps and scares. With Gaius busy, it fell upon Merlin to attend a village stricken by mysterious illness.

Despite having his doubts allayed by Gaius’ pep talk, it was a strange position for the young wizard to find himself in, tasked to deal with an ostensibly non-magical problem. Spun as a good opportunity for Merlin to prove himself to Arthur though, it worked well as a way to bring the characters into a situation.

When the stricken men of Longstead could not be magically healed, the tale promptly moved into more traditional territory, with the returning party waylaid by Gwaine’s heroic instincts and aiding a damsel in distress; a girl who appears to have an almost allergic reaction to Merlin himself.

With Arthur remaining behind, this was a great chance for the lesser Knights to breathe. Percival was more than a little intimidating and Gwaine had his moments too, with a manic gleam in his eye when butting up against Sir Leon. Could this foreshadow future trouble between them?

However, at the village it felt like the story missed a beat. We moved rapidly from talk of ‘something being transported’ to the girl being a Lamia. Also the cure appeared to be simplistic; was it just a remedy that Merlin didn’t know? Either way, Gaius’ info-dump ratcheted up the tension nicely for Elyan’s embrace.

With the Lamia herself, there was an intense performance from Charlotte McKenna, as she moved effortlessly from the pitifully childlike, though temptress and into a fully possessed monster.

The CGI realisation of the creature was impressive too, judiciously minimal and kept mainly in the castle gloom. We have just one nitpick though; for a creature that is so obviously intelligent and scheming, why doesn’t the Lamia choose another name for itself to avoid detection?

As Arthur headed out in search, with Agravaine and Gaius in tow, we had to wonder who was left running Camelot? The young king again demonstrates his abilities yet appears fatally flawed when it comes to Gwen, putting his affections before his responsibilities.

Bradley James plays Arthur’s frustrations well, and we expect to see more of his desire to lead from the front rather than remaining the stately, decision-making monarch.

With no Morgana, and Agravaine reduced to little more than a touch of misdirection, a question remains. Why would slave-traders be transporting such a dangerous creature? Surely Morgana’s hand was in this, or are other dark forces amassing? Either way, it was refreshing to have a week off from the ‘big bad’.

Seeing Gwen escape her servant duties again was a relief and something we have been waiting for all series. Despite all of Arthur’s apparent assumptions, she again proved herself both brave and resourceful. Gwen was beginning to question Merlin’s status too, the reveal of which was teased but again frustratingly denied in the final confrontation.

With superb direction from Justin Molotnikov, Lamia is another great, confident instalment.

Aired at 8.15pm on Saturday 19th November 2011 on BBC One.

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