In a dismal year like this we're often tempted to overpraise a decent film and call it, well, superb; or marvelous, or even, dare I say it, great. "The Constant Gardener" is not great - its slow and elegiac conclusion, a coda to the story, really - is perhaps a bit trite and too heavily foreshadowed. But I truly can't find much else wrong with the film.

An adaptation of John LeCarré's novel of evil doings by a multinational pharmaceutical company in East Africa, in collusion with the British diplomatic service, the film tells its story through the eyes and lives of a married couple - Justin and Tessa Quayle. Justin (Ralph Fiennes) is a midlevel British diplomat stationed in Kenya - not a spy, by the way -who meets Tessa (Rachel Weisz) back in London when she challenges him on Britain's Iraq policy at a lecture he's giving. While the hostile audience tries to shout her down and then leaves, Justin responds in his quiet, tentative way, finding himself attracted to her. Soon they're in bed together; and shortly after they're married and back in Nairobi, he to his office and Tessa to her field work with a doctor (Hubert Koundé), treating women and children who are HIV-positive.

But the film is not so straightforward; it begins, in fact, with Tessa's death in Africa and becomes the story of Justin's hesitant, confused search for clues as to how and why she died. And it is told in fragments, a collage of scenes and moments that go back and forth in time and little by little add up to the truth. Collage films rarely work, but when they do, as they do here, they can make for great cinema.

Rachel Weisz's performance is a miracle, surely the best of the year to date: Tessa is tormented by itches sexual and political; she can neither hold still nor be a good diplomat's wife. She never shouts but breathes out her needs with a soft laugh and laser eyes that cannot be denied. Weisz deserves every possible award for her work; we can only hope it will be remembered at the end of the year. And Fiennes, who sometimes seems to rely on screen presence rather than the making of a character, has pulled his Justin back, softly, into the shell of a passive man not unacquainted with being humiliated, even by those he calls his friends. And yet we can see the fierce love he has for Tessa and even the reason she chooses to marry him.

Now we can add to these performances - and those of Danny Huston as Justin's boss and best friend; Bill Nighy and Pete Postlethwaite as two key players - the direction by Fernando Meirelles, the young Brazilian master who made the breathtaking "City of God" three years ago. Meirelles has shot the film (with his cinematographer César Charlone, who shot "City of God") almost like a documentary. The rush of fragmented scenes, with hand-held cameras that are never overused or call attention to themselves, sustain both the frantic pace of Tessa's and Justin's lives and the race to solve the mystery surrounding her death. Moreover, the screenplay, by Jeffrey Caine, has the wit and intelligence not to rely on conversations in which the plot points are laid out for us. As the scenes are fragmented so is the dialogue; words are overheard, half-heard, remembered and called up later. One of the most erotic - and politically charged - scenes in the film depends more on pauses than on language. "The Constant Gardener" is a rare find indeed; perhaps the best film of the year to date.