From John Wayne's gung-ho "The Green Berets" to Randall Wallace's revisionist "We Were Soldiers", dozens of films have tackled the Vietnam War.

Very few, however, have explored the conflict's roots.

Set in Saigon in 1952, Australian director Phillip Noyce's superb political thriller based on Graham Greene's prescient novel does precisely this.

The film takes place against the backdrop of the Vietnamese struggle for independence from French colonial rule.

Despite the conflict, British journalist Thomas Fowler (Caine) enjoys a pleasurable existence with his beautiful young Vietnamese mistress Phuong (Yen).

But his complacency is disturbed by the arrival of idealistic American aid worker Alden Pyle (Fraser).

At first, the cynical Fowler observes the newcomer's zeal with detachment. The seemingly naive Pyle is seeking to promote a third force in the region, one that is neither colonial nor communist.

Fowler, however, doesn't take sides: "I don't get involved," he says. "I just report what I see."

But when Pyle attempts to take Phuong away from the older man, at the same time as violence explodes on the streets of Saigon, Fowler's neutrality is shaken. Now he must decide just where he stands...

Greene's novel has been filmed before. But Joseph L Mankiewicz's 1958 version downplayed the book's attack on US meddling in the region - much to Greene's fury.

Noyce's measured, intelligent film, however, restores the novel's political and moral complexity.

Noyce is helped by a terrific cast (Caine, in particular, excels as the world-weary reporter), and by Christopher Doyle's stunning cinematography, which captures Vietnam's humid, misty climate in all its subtle shades.

It isn't only the light in the tropics that renders things ambiguous, however. In Greene's world, the workings of the human heart are equally murky.