The Constant Gardener (15)

With his kinetic editing and taste for harshly coloured textures, Meirelles may be an aggressive stylist, but he can also be subtle, using style as eloquent metaphor. The film begins with British diplomat Justin Quayle (Ralph Fiennes) saying goodbye to his wife Tess (Rachel Weisz) and her doctor companion Arnold (Hubert Koundé) at an African airport. As the pair walk towards their plane, the background bleaches into hazy white and they disappear into uncertainty - it's the last time Quayle will see them alive and the rest of the film details his attempt to restore focus to the blur, to learn what happened to them. and, indeed, to find out who his wife really was.

The Constant Gardener is a characteristic Le Carré drama of benign etiquette over the table, cold-blooded corruption underneath. Fiennes's Quayle is a tender, ineffectual decent sort among the stuffed shirts of the British High Commission in Nairobi, whose genteel customs protect them from a morally unhygienic world they'd rather not sully their hands with. The problem for Quayle is that Tessa sees it all: apparently an Amnesty worker, and more generally a freelance agitator for uncomfortable truth, she can be relied on to flout protocol at parties and ask awkward questions of Kenyan politicians and British businessmen alike - to make a fuss, don't you know. That's why she's found dead in a jeep by the side of a desolate lake (Meirelles spares us the brutal forensic details that the novel spells out).

At once detective intrigue, revenge drama and love story, The Constant Gardener intelligently covers both personal and public fronts: it makes Quayle credible in his progress from mild-mannered apparatchik to impassioned crusader; and it makes you think about what Western business interests are doing to Africa, the plot's payoff being a pharmaceutical intrigue in which African lives are regarded as disposable lab equipment.

With a fine-tuned cast and a complex, economical script by Jeffrey Caine, the film has a keen ear for the language of British diplomatic hypocrisy. We hear all the usual Le Carré mantras - the references to discretion and the "proper channels" - yet somehow we feel as if we're relishing their absurdity for the first time. Thus a scene which might have registered as a dutiful nod to the Tinker Tailor Soldier Spy tradition comes out relishably crisp: Quayle at a London gentleman's club, offhandedly cautioned by Bill Nighy's weaselly Whitehall mandarin in a tart little ritual of rank-pulling over the sole meunière. This is a world in which the most ominous threats are often couched as affable apologies on the golf course.

The film is astute, narratively and commercially, in mixing its geopolitical anger with a story of love staring death in the face. Its romantic twist is that the bond between Justin and Tessa is only truly consummated after her murder, when her memory has led him to the centre of the maze (the intrigue recalls the TV eco-drama Heart of Darkness, with an intrepid hero doggedly nosing towards the molten core of catastrophe). This is, among other things, an elegant romance between two intelligent people who, after sparking an instant amour fou - its sex scene gracefully montages close-up body parts - effectively misunderstand each other until too late.

The pair have a bright, unusual dynamic: Fiennes's gently pained, cautious tenderness as Justin is nicely counterpointed by Reisz's sweetly confrontational style. Her Tessa is more complex and elusive than the off-the-peg firebrand she initially seems, and Weisz's flair for mischief lends itself perfectly to this black comedy of manners.

She has a wonderful scene with Danny Huston, as Justin's colleague Sandy Woodrow; this patrician actor's pampered jowliness has never been more effective than in this concise unfolding of his character's duplicity. When Tessa teasingly offers Sandy sexual favours in exchange for a crucial document, Huston's cautious cat-got-the-cream double-take is priceless: "Are you serious?". Towards the end, the film strives too hard to deliver a rattling yarn.

Quayle arrives in Sudan to track down a key player just at the very moment that a raid by hostile tribesmen bursts over the dunes - the only bad moment of blockbuster rhetoric. But Meirelles and cinematographer Cesar Charlone capture telling details that are just on the right side of postcard-memorable: such as the shot of an African child running under the shadow of a departing plane's wing. The visuals only verge on cliché in the treatment of a London in the familiar steely-blue mould of CCTV-ridden secret-state narratives; still, this makes for a nice contrast with the rusty chemical reds of the Nairobi skyscape and the parched desolation of Lake Turkana. If the film does sometimes err on the side of brochure-like local colour, it does at least set out to tell us that its British protagonists are surrounded by a Kenyan culture that has its own life and meaning - unlike Andrew Niccol's recent satire Lord of War, which really did use Africa as a throwaway backdrop. Meirelles's British-produced film is classy work, intelligent, passionate and vibrantly made - not a blockbuster, more the upmarket screen equivalent of the thinking person's airport novel.

j.romney@independent.co.uk