The Dark Knight (12A)

The joke's on this superhero

Those suffering from a fear of heights should have a care on entering the new Batman movie, The Dark Knight, for its opening shot looms with a precipitous shock that could make you queasy.

The massive Imax screen on which I saw it made Lilliputians of the audience, dwarfing us within the vertiginous perspectives of gleaming skyscrapers and towers, from which the drop looks terrifying.

The city is Gotham, and the metaphor couldn't be clearer: we are on a moral precipice. Director Christopher Nolan and his co-screenwriter, his brother Jonathan, having established the origin story of Batman Begins (2005), have draped this follow-up in deeper shadows and darker ambiguities. Does Gotham have a protector after all, or is Batman just a vigilante in a cape?

The film seems to be offering us a hero who wants to hand in his notice. The tension of Batman's double life, between his public face as playboy tycoon Bruce Wayne and his private mission as urban crimebuster, is tearing him up inside. He has become a prisoner of his Bat-mask, the one he cannot remove lest – well, lest the mystery dissolves and Warner Bros let slip a golden franchise. (The advance ticket-sales alone for this movie are staggering.)

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What we know that Batman needs is an adversary worthy of him, and while Jack Nicholson's leering showman cut some memorable ham in the Tim Burton movie of almost 20 years ago, he now looks quite tame next to this one's incarnation.

It is difficult to watch Heath Ledger as The Joker without being reminded that this was the actor's last complete performance before he died in January, aged 28. I'm not sure that it's the Oscar cert some have proclaimed it, but it certainly leaps off the screen. "What doesn't kill you makes you... stranger," he muses in his odd, loose-tongued, drawl.

His face white with flaking powder, mouth a smeary scarlet rictus and eyes blazing coals of malevolence, this Joker is indeed stranger, robbing and murdering without discrimination, bent on making merry hell just for the sake of it. You always know the real bad 'uns in films when, at the end, they treacherously kill their own henchmen. This guy, on the other hand, begins by killing his henchmen, right after they've helped him stage a spectacular bank robbery. If the rule is never to negotiate with terrorists, what to do with a terrorist who sees nothing to negotiate?

Batman, meanwhile, the Dark Knight of the soul to the Joker's twitchy lord of misrule, longs for someone to step up to the plate as Gotham's "hero with a face", and thus free him to pursue the love of his life, Rachel Dawes (Maggie Gyllenhaal). That hero might be at hand, in the shape of district attorney Harvey Dent (Aaron Eckhart), a crusader who first made his name flushing out bent cops; now he aims to take on the Mob, represented here by the not-quite-human-looking Eric Roberts. All that's keeping Bruce/Batman from pledging his support is the tormenting knowledge that the doughty Dent is romantically involved with Rachel.

Their screentime together is part of a deliberate tendency on Nolan's part to make the movie an ensemble, rather than a one-man, show. Christian Bale, elegantly brooding if a touch humourless, has a hard job lending any variation to Batman's expression with only his chin and mouth to work with, and his voice is too gravelly not to seem an obvious disguise. At times he's just another member of the cast, competing for attention alongside Bruce's paternalistic butler (Michael Caine), his gizmo expert and quartermaster (Morgan Freeman), and his closest ally on the police force, Lieutenant Gordon (Gary Oldman).

They are all eventually upstaged by The Joker's elaborate psychotic pranks, which include kidnapping, assassination, blowing up hospitals and inciting people to mass murder – it's all in a day's work for him. As someone says, in the wake of his latest outrage, "Some men just want to watch the world burn." The resonances with our own climate of fear are never explicit, but they are undeniably present. In the last third of the film the mood darkens still further when a force of good turns, agonisingly, to bad.

It is no small irony that The Dark Knight, obsessively concerned with doubleness and duplicity, should itself emerge as a two-faced proposition. Nolan, whose key film is the fractured amnesiac thriller Memento, touches on areas of psychological dread and doubt that hardly seem containable within a blockbuster. Yet, also to his credit, he never forgets that a blockbuster is what he has been hired to deliver.

Art and entertainment feel locked in a deadly struggle, which accounts for the movie's peculiar schizoid personality. Just when it poses its most heart-stopping question – how do you tell a loved one facing imminent death that "everything's going to be all right"? – it swerves into a maniacal car chase, with our hero now hot-rodding a vehicle known as a Batpod, a kind of monster-truck tyre with a seat. The ear-lacerating volume and the automotive mayhem that attend these action sequences seem to be doing everything possible to shake whatever subtleties that may have entered one ear straight out of the other.

You will exit the cinema with an enhanced respect for Nolan's intelligence, for Wally Pfister's pin-sharp cinematography, and, sadly, for an acting talent tragically curtailed. Ledger has left us with a performance both to please and disturb, and the sad irony will perhaps be registered that the biggest laugh his Joker gets is poised on a single word: "Hi."