Unless you happen to be young enough never to have encountered any version of Arthurian legend before, the themes of this week’s episode will come as no surprise.

Merlin has to hit certain beats in the myth to tell the tale and for us, as we imagine for many viewers, the fun comes from seeing quite how they achieve it within the constraints of family viewing.

Following on from Arthur’s apparent awakening to Gwen’s bravery, as well as her wisdom and salt-of-the-earth nobility, he resolves to propose to her in defiance of Agravaine’s wishes.

This, of course, sends dear old Uncle scuttling off under the cover of darkness to his mistress once again. In retaliation, Morgana initiates a plan to strike right at the emotional core of Camelot, ensuring that her prophetic vision of Queen Gwen may never come to pass.

One might question the apparent ease with which Morgana achieves the resurrection of Lancelot, but it would be churlish to focus on that. This episode truly turns on the emotional drama generated between Arthur, Lancelot and Gwen. So much in fact that, other than some wisecracks, there is very little dialogue for any of the other young cast members at all!

As the relationship drama unfolds there’s a jousting contest too, which is well handled and helps to ramp up the tension. In many ways it harkens back to earlier series where Uther would preside over such events, which is appropriate given his feelings on the union of Arthur and Gwen.

The romantic leads Bradley James and Angel Coulby run us though a gamut of emotions, from joy to despair, in quite spectacular fashion. Arthur’s explosive anger flares wonderfully before fading into a colder, grim reality as he grapples with the result of Gwen’s actions. For her part, Angel Coulby shows us a broken Gwen who’s truly distraught. Santiago Cabrera’s Lancelot is brooding and intense as ever, truly credible as a rival for Gwen’s affections.

The method in which Gwen’s loyalty is tested and her resolve broken is an interesting path to take. Furthermore, the writers choose to hold back part of the revelation even from Merlin and we can’t help but wonder if this will come to light further down the line.

With the young wizard suspicious of Lancelot’s return from the outset, Merlin is very much on the outside looking in as this drama unfolds. He has damning suspicions but no evidence once again.

Colin Morgan plays it beautifully, thrilled at the sight of his friend’s happiness and despairing when it all goes awry. If the heartbreaking scenes between Arthur and Gwen don’t grab you, then we guarantee Merlin’s final scene will.

It’s hard to recall an episode of Merlin that has been more compelling to watch, or one whose ramifications on the overall story will be felt more. Tremendous.

Airs at 8.15pm on Saturday 26th November 2011 on BBC One.

> Order the Complete Series 4 boxset on Amazon.

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