Christian Bale has been on a diet again. Not satisfied with losing four stone for The Machinist he's shed 100lbs to play American flyboy Dieter Dengler.

The cocksure fighter pilot found himself Vietnam's Slimmer of the Year when he was shot down over Laos in 1965 and banged up on a diet of weevil-ridden slop in a makeshift jail.

German director Werner Herzog first told Dengler's story in the highly-acclaimed 1997 documentary Little Dieter Needs To Fly.

This time he fictionalises the story of the flier, a tough, resourceful individual brought vividly to the screen by Bale who underlines his commitment by chomping down maggots and munching on live snakes.

After crash-landing in the dense jungle, Dengler is captured and finds himself in a decrepit prison camp alongside fellow Americans, the broken Duane (Zahn) and unbalanced Gene (Davies).

Their gaolers are a reluctant crew of farmer-guerrilla fighters whose careless indiscipline lends them the perfect opportunity to escape. But where to?

The jungle in the fetid atmosphere of the rainy season is its own prison and the escapees find the going tougher than they could ever imagine.

While the theme may be familiar, Herzog's treatment of Dengler's plight is given grim authenticity by evoking the jungle as a genuinely hostile place with Mother Nature the most brutal gaoler.

With the unconventional German at the controls, there's also little danger of this descending into a flag-waving backslapper a la Behind Enemy Lines.

For fans of visceral, lean and taut cinema, this is an object lesson in power and economy.

Tim Evans