While their elder siblings visit the USA with their parents, Lucy (Georgie Henley) and Edmund (Skandar Keynes) are stuck staying with their odious cousin Eustace (Will Poulter). Lucy and Edmund are thrown back into Narnia, where King Caspian (Ben Barnes) is on a voyage to find the seven missing lords. Much to their dismay, Eustace comes along for the ride.

After Prince Caspian endured a less successful theatrical run that anticipated – and Walt Disney Pictures and Walden Media fell into an intractable disagreement over production budgets – the entire Narnia franchise jumped ship over to 20th Century Fox for its third instalment: The Voyage of the Dawn Treader. (Amusingly, since buying out Fox part and parcel, Disney now owns all three films.) In keeping with the original novel by C.S. Lewis, Peter and Susan are out of the picture and Lucy and Edmund are promoted to leads.

Both Georgie Henley and Skandar Keynes have aged five years over the course of making the three Narnia films, and in Dawn Treader they put that experience to good use. Henley in particular shines, playing out some strong character development and grabbing her expanded role with both hands. Newcomer Will Poulter makes for a pitch-perfect Eustace, bring a superb level of comedy to the role. Having first seen him in the BBC’s sketch series School of Comedy and more recently watching his career blossom through Detroit and Midsommar, it is wonderful to see his talents be put to such good and varied use. This is the last of Narnia films, and is honestly is a tragedy that Poulter did not get the opportunity to play a more mature and responsible Eustace in The Silver Chair.

Ben Barnes is back as Caspian, now king, and has somehow lost his Spanish accent in the change of studios. He is still effective, in a bland sort of way, but here he feels more of a generic swashbuckler than the slightly more developed version last time around. Speaking of swashbucklers, the sword-fighting mouse Reepicheep, voiced splendidly in Prince Caspian, returns with the voice of Simon Pegg – nowhere near as effective. I suspect it’s only Australians who will be amused by the presence of TV star Gary Sweet as Caspian’s first mate, but he acquits himself well as long as you forgive the uneven Irish accent. Much of Dawn Treader was shot in and off the coast of Australia, so in addition to Sweet viewers also get to see genre legend Bruce Spence, Bille Brown, and other local talents. Less satisfactory is an illusory cameo by Tilda Swinton as the snow witch Jadis, which pretty much exists solely to get Swinton onto the film’s poster and fool audiences that she’s actually in the film.

The visual effects feel a little cheaper and less impressive on the third trip around – possibly the result of budget cuts – but the design aesthetic remains strong. Plotwise, the film struggles. The original novel is a simple episodic affair, with the crew of the Dawn Treader visiting island after island and uncovering each Narnian lord in turn. What works on the page does not necessarily work on screen, and the woolly plot structure robs Dawn Treader of much of the previous films’ energy. The result is a film that works nicely on a scene-by-scene basis, but struggles to maintain an overall quality. Of the three Narnia films, this is sadly the least accomplished. Part of the problem may be the appointment of Michael Apted – a superb documentarian but often a lacklustre narrative filmmaker – as replacement for Andrew Adamson as director.

The film unfortunately ends on the tedious chore of Aslan the lion (Liam Neeson again) returning and delivering a thinly veiled religious sermon aimed at converting Narnia fans to Christianity. It has lurked around the edges of the previous two films, but in this third effort the film goes for broke: pointing emphatically at Aslan, his elusive kingdom, and how Lucy can ever seen him again, and as good as silently mouthing ‘Jesus’, ‘heaven’, and ‘go to church, children’ at the audience. In the film’s defence it is only working to what Lewis intended, and as a company owned by religious conservative Philip Anschutz Walden Media specifically exists to bring these kinds of books to the cinema. Even with that in consideration, it is a pushy and morally suspect way to proselytise.

It is sad that Narnia, in this iteration at least, ends on such a whimper. The lack of a fourth film was not, as many suspected, because of poor box office. Walden Media lost the rights to Lewis’ books while an adaptation of prequel The Magician’s Nephew was in pre-production. It’s a shame: there is a great potential in both that book and The Silver Chair – and hopefully that would have been it. Trust me that no one would have benefitted from films of A Horse and his Boy of The Last Battle.