WHEN you least expect it, cinema transcends its role as escapist entertainment and manages to spark debate and even change the world.

Michael Moore's documentary Fahrenheit 9/11 launched a blistering attack on the American government for its role in the September 11 tragedy and Morgan Spurlock's similarly controversial Super Size Me compelled millions to turn their backs on fast food.

Mel Gibson's brutal Passion Of The Christ sparked heated debate and religious protests, and Spielberg reminded us of Europe's darkest days in his Oscar-winning opus Schindler's List.

Edward Zwick's Blood Diamond purports to be a thriller with a conscience, wearing its politics on its sleeve to highlight the trade in conflict diamonds, which are smuggled out of war-ravaged countries and used to buy weapons to perpetuate the cycle of violence and bloodshed.

The film's intentions are honourable but in truth, the fast-paced action sequences and starry performances overwhelm any worthy, underlying message.

During Sierra Leone's brutal and bloody civil war in 1999, fisherman Solomon Vandy (Hounsou) watches helplessly as rebel forces decimate his village, taking him hostage to work in the diamond fields while his beloved wife Jassie (Mabhena) and son Dia (Kuypers) flee, heading for the border.

For weeks, Solomon is subjected to physical and verbal abuse at the hands of Captain Poison (Harewood), who ensures the captives sift the muddy river waters, looking for gems to finance the country's arms trade.

Before escaping his hellish ordeal, Solomon unearths a priceless pink diamond and hides the gem close to the river.

The existence of such a large stone arouses the interest of Zimbabwean smuggler Danny Archer (DiCaprio).

Solomon agrees to accompany Danny back to the war zone, only to cross paths with crusading journalist Maddy (Connelly), who is writing an article on the underground trade in diamonds for guns.

The three strangers become embroiled in a race against time to retrieve the stone and to reunite Solomon with his loved ones.

Blood Diamond begins promisingly, moving from the bloody assault on Solomon's village to introducing the cynical and money-oriented Danny and the holier than thou Maddy, who clash over the smuggler's exploitation of Solomon.

"I am using him, you are using me - this is how it works," replies Danny.

Performances are strong - notably Hounsou as the father of great strength and nobility - and DiCaprio holds our attention, despite an accent that evaporates mid-sentence.

Tension escalates in the final hour when the film reveals itself as a conventional chase movie, with Danny and Archer risking everything to evade Poison's henchmen, and the script piles on the soul-searching and earnestness.

"I wonder, will God ever forgive us for what we have done to each other," says a teacher as the three protagonists head into the jungle. "Then I look around and I realise - God left this place a long time ago."