Rescue Dawn (12A)

An almost unrecognisable Christian Bale turns in a truly extraordinary performance in Werner Herzog's real-life tale of an escape to freedom through the jungles of Laos

Christian Bale – now there's a glutton for punishment. Daniel Day-Lewis? Robert De Niro? Mere boulevardiers compared to him. Bale muscled up for the dragon-fighting fantasy Reign of Fire, lost 63lb to play the skeletal hero of The Machinist and bulked up again for Batman Begins. Now he's back on the skin-and-bone regime in Rescue Dawn, Werner Herzog's drama of survival in extreme jungle conditions. Give the man a break: he's earned his right to play a restaurant critic.

Furthermore, Rescue Dawn sees Bale buffeted on a raging river, dragged along the ground by an ox, immersed in a well, hung upside-down tied to an ants' nest. There are stunt doubles listed in the credits, but working with Bale, they probably had more downtime than they expected. Rescue Dawn is considerably more than the Boys' Own S&M adventure this might suggest, but the authentic torment for which Bale and Herzog are sticklers is very much an issue of ethics in the era of CGI illusion. For Herzog, the sense of film-making as a genuine, and genuinely risky, human activity – as an adventure in the exalted, almost spiritual sense – has always been foremost.

Rescue Dawn narrates the real-life ordeal of German-born US Navy pilot Dieter Dengler, a PoW in Laos around the start of the Vietnam War. Herzog has told this story before, in his 1997 documentary Little Dieter Needs To Fly; presumably he felt the need to get deeper inside Dengler's ordeal by having actors not just recreate it but effectively relive it. His first fiction outing since the 2001 misfire Invincible, Rescue Dawn may not display the grandiose vision of such vintage Herzog exploits as Aguirre or Fitzcarraldo, but the extremity of the undertaking is comparable. At moments, even Fitzcarraldo's objective, to drag a ship up an Amazon hillside, pales besides this emaciated cast's achievement in merely standing upright.

The film begins with Dengler setting out on his first flying mission, a bombing sortie into Laos in 1965. When his plane is shot down, Dengler runs for cover in the Laotian countryside, a place so intensely green – its colour booted right up in Peter Zeitlinger's photography – that it resembles an alien world (Herzog's last release, the quasi-documentary The Wild Blue Yonder, made it clear that for him, Earth truly is another planet).

Captured by Vietcong – almost uniformly depicted as screeching sadists – Dengler is interned in a jungle camp with a handful of Asian prisoners and two Americans, Duane (Steve Zahn) and Gene (Jeremy Davies). This pair, captives for some time, offer a terrible warning of what could await Dengler: they're skeletal and sunken-eyed, both actors matching Bale rib for rib in the dieting stakes. The babbling, demented Gene is a role that Jeremy Davies is made for, having specialised in screen crazies for several years. Here, though, he's truly imposing, Gene's scared, twitchy madness coming across as the authentic scar tissue of deprivation.

Dengler's co-prisoners have little faith in his escape plans, but he hasn't yet had his will broken, and startles them with his cheerful, no-nonsense artisanship. He makes a first move towards stealing back freedom by the simple expedient of stealing a nail, and uses wood and pebbles to make a surveillance "map" of what's going on at the camp.

The film is not only meticulously precise in its account of escape procedure, it's also very economical in evoking the way that captivity shrinks the soul: we see Gene longingly ogling an old bean-tin label, the starving man's equivalent of a Playboy centrefold. Dieter's attempt to boost esprit de corps pays off on his birthday with a toast of makeshift "champagne", made from crushed insect larvae. There's a certain horror aspect to the film – a Bush Tucker Challenge element – and Bale's ability to look chipper while gobbling a fistful of live maggots is testament to his whole-heartedness. But all this only means anything in so far as it does justice to the horrors that Dengler and co endured.

The drama becomes increasingly gripping as the stakes rise, as Dengler and Duane make their dash for it, struggling not only with the jungle but also with their own fatigue and flagging sanity. Looking practically blue by the end, as if already mouldering, Steve Zahn really comes into his own here, in an immensely touching performance of slow collapse. He has long been one of Hollywood's most underrated and watchable actors, ever since Reality Bites, but here he's a revelation as a shaggy, withered shell of a man whose vulnerability is partly what motivates Dengler to survive and protect him.

Herzog's films, especially where man and nature are involved, are usually pessimistic, but Rescue Dawn marks a distinct change: Dengler, as we know, survived to tell his tale, by all accounts with his mind and his humanity intact. The most characteristically Herzogian image here is of Bale's eyes, staring ferally from a bush, yet Dengler is saved from the brink of the abyss.

It's his seemingly impossible simplicity and tenacity – which Bale conveys with charismatic energy – that keep him alive. At the root of Dengler's indomitable character, it's suggested in passing, is the childhood experience of surviving the Second World War in Germany. The film ends with a disastrously jarring shift of tone, a brazenly gung-ho coda that tries to sell the film to us as a tribute to all-American endurance and know-how, but don't be fooled. Herzog is actually celebrating German will and technical brilliance: his hero's and his own.

Need to know

Werner Herzog acquired his first 35mm camera by stealing it from the Munich Film School. Known for never using storyboards and often improvising large parts of his scripts, he became central to the German New Wave movement. His films include the sci-fi hit 'The Wild Blue Yonder' and 'Grizzly Man', a tale of the environmentalist Timothy Treadwell who was killed by the bears he lived amongst in Alaska. Herzog, 65, had to battle to get his own way on 'Rescue Dawn', his first Hollywood-funded feature.

This week Jonathan Romney has been reading The Three-Arched Bridge by the prolific Albanian novelist Ismail Kadare: 'his ability to spin eerie parables out of a little-known national history makes his books an addictive pleasure'

Further reading 'Stranger than fiction: the real-life adventures of the auteur-adventurer' in 'Herzog on Herzog', edited by Paul Cronin (Faber)