The opening instalment of Series 4’s two-part finale brought us comedy, sorrow and an act of dark betrayal before the opening credits had rolled. Ten minutes after that, Camelot had fallen.

As Arthur prepared to celebrate Beltane with his knights, the forces of Helios, Southron Warlord and new ally of Morgana, amassed outside the city. With the aid of their inside man, city defences were left wide open and our heroes soon found themselves fighting for their lives.

In short order, Merlin spirited a wounded Arthur away leaving Camelot at Morgana’s mercy as the tale became one of a road trip, with the pair hunted by Agravaine through the forest.

Merlin’s magic amusingly recast Arthur in the role of ‘simpleton’ for a time, turning their master and servant relationship on its head to great comic effect, Later, once freed of the enchantment, there were some thoughtful moments with Arthur suffering a dark night of the soul and Merlin endeavouring to reignite his fighting spirit. Once again this was beautifully played by the two lead actors.

The insidious Uncle’s moment of treachery finally came and Nathaniel Parker did it in style, torching the town and leading a band of Southron men into the palace. Soon sensing that Helios had supplanted him in Morgana’s affections though, his tone shifted markedly from smug to desperate.

Now engaged in the task to track down Arthur, we appear to be heading for Agravaine’s final moments. If so, we hope he will have a suitably dramatic send off, staying true to his cause and without a last minute change of heart.

The introduction of Tristan and Isolde was a surprising move. Far from the legendary characters of a Cornish Knight and his forbidden Irish princess lover, they have been translated into a pair of loved up smugglers.

Presenting as a rugged Han Solo type and his muse, Tristan (Ben Daniels) and Isolde (Spooks alumni Miranda Raison) appear to be a well matched and likable pair with their relationship styled to provide inspiration for the healing of Arthur and Gwen’s rift. With their counter-culture lifestyle loyalties too, it will be interesting to see what other contribution either might make should they be around for the long haul.

Female characters were well employed for once, because as well as the introduction of Isolde, Morgana (Katie McGrath) finally got to wield some power. She may have spent the better part of this series scheming in the shadows, but soon made up for it by torturing Elyan and making Gwaine ‘perform’ for her entertainment. It was great to see her unleashed.

Also, there was a welcome, if brief, return for Merlin’s mother Hunith as he took his pursued gang to her village of Ealdor. Let’s hope Merlin has not put her into danger by leading Agravaine to her door. Gwen’s reunion with Arthur was a touching moment too, also cut short by the hunting party’s arrival.

With some great imagery at play, such as the torchlight wielding forces of Helios surging across one of Camelot’s precincts, director Alice Troughton kept the episode well paced, if perhaps a little heavy on the slow motion shots. However, with no sight of either the title’s sword or stone yet, it appears this tale has plenty to do in its final half. Part One was certainly an enjoyable start.

Aired at 8.10pm on Saturday 17th December 2011 on BBC One.

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