Harry Potter and the Deathly Hallows: Part 1, David Yates, 146 mins (12A)

If you haven't read the books, the latest Potter plot will whizz over your head like a broomstick

The flaw in the last couple of Harry Potter films was that, rather than being discrete stories, each was one-seventh of a much longer story. Harry Potter and the Deathly Hallows Part 1 is different: it is one-fourteenth.

JK Rowling's final novel has been split into two films, so in two-and-a-half hours all we get is one-half of one-seventh of the series. No wonder it's unsatisfying. A "previously on Harry Potter" caption wouldn't have gone amiss, but HP7 doesn't make the slightest concession to viewers who aren't already conversant with its byzantine mythology, its ever-expanding throng of characters or its bewildering range of spells and totems. If you don't understand the question, "Did R.A.B. destroy the real Horcrux?", then most of the film will fly over your head like an enchanted broomstick. Still, at least HP7 makes some strides towards a finale. The first of the films not to be set in Hogwarts School of Witchcraft And Wizardry, it gets going just as the battle between good and evil is escalating to all-out war.

Voldemort (Ralph Fiennes) and his crowd of followers have decided that the time is right to kill Harry (Daniel Radcliffe), so he and his faithful if grumpy sidekicks, Ron (Rupert Grint) and Hermione (Emma Watson), go into hiding in the countryside. When they're not bickering with each other or tramping through the woods, they try to find the talismans that hold the key to Voldemort's power. And then, just in case they didn't have enough vitally important trinkets to gather, they hear about three more, known as the Deathly Hallows.

The gang's quest may seem as arbitrary as the token-collecting in a video game, but it does provide a pretext for one outstanding set-piece. Disguising themselves as adults (not too difficult), Harry and co sneak into the Ministry of Magic, a gleaming black labyrinth of offices which, under Voldemort's influence, has become an Orwellian fascist bureaucracy, complete with 1940s-style posters denouncing racial impurity. This fast, farcical heist sequence could easily have been the centrepiece of the film, like the rescue of Princess Leia from the Death Star. But unfortunately there are about 23 other plot snippets to fit in, too. As a whole, the movie is a long, exhausting trudge, weighed down by its gloomy mood and its lack of heroics. Harry's most significant achievement is to locate a magical sword, but that happens only because a ghostly stag (a "Patronus", I'm told) pops up and leads him straight to it. Surely that's cheating.

Maybe we shouldn't blame the film's director, David Yates, for all of its shortcomings. By the time he climbed aboard, the Harry Potter gravy train had been trundling along for years. Other directors had already established that the films would be literal, scene-by-scene translations of the books, however unwieldy that made them. And the cast was in place before Yates's tenure, too, so it's not his fault that Radcliffe is so lifeless, or that Watson doesn't appear to be acting so much as responding to someone who's just off-camera, shouting: "Now put on a sad face! Now put on an angry face!"

Joining this pop-cultural juggernaut after a career in television, Yates was never likely to upset the status quo by arguing, for instance, that the story would flow more smoothly if it missed out Rhys Ifans's Xenophilius Lovegood. Or that if you're going to insert John Hurt into a dungeon scene, someone should explain what he's doing there. Or that, in general, none of the excellent character actors – Alan Rickman, Imelda Staunton, et al – is given enough to do.

But while Yates may not be solely responsible for the way the franchise has turned out, his three films – this one and the previous two – are the only ones which don't make sense unless you've swotted up on your Potter lore in advance, so they do raise the question of how another, bolder director might have reinvigorated the series.

It seems that Yates's only goal was to get all the key scenes down on screen in the correct order, and he does that well enough to keep the fans happy. What he's made isn't really a film at all but a lavish set of book illustrations which are a splendid visual accompaniment to Rowling's text, but which don't mean much without it.

Next Week:

Nicholas Barber sees whether Unstoppable, Ridley Scott's Denzel Washington-vs-runaway-train thriller, lives up to its name

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