In the moral vacuum that is an imploding Sierra Leone, diamonds are a gunrunner's best friend.

The merchant of death in question is Danny Archer (DiCaprio), a South African army veteran who's adapted his soldiering skills into smuggling gems out of the war-torn country via neighbouring Liberia.

The grenade launchers and machine-guns he exchanges for the dodgy sparklers then find themselves in the hands of a ill-disciplined "revolutionary" rabble, some still in short trousers.

When he discovers that Mende fisherman Solomon Vandy (Hounsou) has hidden a priceless pink diamond just before liberation from a rebel-run slave labour camp, he sees it as his ticket out of the country.

However, he's not alone. Rebel RUF leader Captain Poison (David Harewood) and government commander The Colonel (Arnold Vosloo) both realise its value and are determined to get their grubby mits on it.

Rattling along at a cracking pace, director Edward Zwick's morally complex action thriller is rewarded by first class performances from DiCaprio and Hounsou.

Solomon is the moral centre of the story around which characters ranging from the rootlessly opportunistic Archer to ethically-challenged Antwerp diamond merchants dodgily vacillate.

The obligatory - but frankly unnecessary - love interest is provided by Jennifer Connelly's hardened foreign correspondent...but she seems shoed in merely to facilitate a redundant conspiracy sub-plot.

The real story revolves around Archer and Solomon and takes in the appalling plight of 10-year-old boys - literally "infantry" - who are snatched by the rebels, drugged up to their eyeballs and fed Marxist claptrap before being handed a Kalashnikov.

This is where the film is viscerally burnt onto the memory as these kiddiwink killers wade through the pampas grass spraying hapless villagers with white hot metal.

Carefully weighing some splendid action sequences - check out the helicopter gunship wasting a rebel diamond operation - against a story that intelligently acknowledges there are no moral absolutes, it's a yarn that rarely talks down to the viewer.

When faced with the spirit-sapping anarchy of Sierra Leone in meltdown, you're forced to concur with the world weary Archer: "TIA - This is Africa".

Tim Evans