The latest in a spate of movies that take the West to task for its indifferent foreign policies, Fernando Meirelles’s thriller “The Constant Gardener” is both the most outraged and the best made of the broad group.

Adapted from Cold War spy-master John le Carre’s book of the same name, the film weaves a murder mystery around the deplorable treatment of Kenyans by the made-up drug company KDH. Barely masking truth with fiction, Meirelles’s portrayal of the pharmaceutical industry is right-on-the-money and, as a result, genuinely horrifying.

But what makes the film so good is not its finger-pointing politics but a keen examination of the American and European apathy that leaves needy countries without help. “The Constant Gardener” is an eloquent parable about what it takes in this impassive age to make a “civilized” man become an activist.

Our man is that impeccable British emoter Ralph Fiennes (“The English Patient”) as spineless diplomat Justin Quayle. Somehow, during a pointed London lecture on the politics of the Iraq War, he manages to snag the heart of a fire-and-brimstone liberal in the audience. Tessa (Rachel Weisz) overpowers Justin with her smarts and beauty; they leave for Kenya as husband and wife.

Once there, Tessa’s heartfelt, often extreme politics lead her to dig deep into the suspicious death of several AIDS patients (much to the chagrin of British spies and pharmaceutical kingpins). In the film’s opening, she is found thrashed and burned in an overturned truck; from there, extended flashbacks flesh out the events leading to her demise.

Relying on the ominous beat of African drums and the claustrophobia of shaky close-ups, Meirelles handles the tale with taut grace. Under his intimate camera work, Weisz and Fiennes bloom. They react to each other with a shy affection rarely found outside of home movies. Meirelles heightens this intimacy by focusing on Justin and Tessa as living bodies. He frequently isolates their forms in washed out frames, exaggerating their physicality (Tessa’s pregnant belly plays a large role in one great scene). This slight surrealist tendency is expressed throughout “Gardener,” adding much needed depth to the otherwise dry storytelling.

In addition to his elegant visual sense, Meirelles is able to navigate between the violent and intensely personal. For example, when Weisz appears in several later scenes of the film as a ghost, it isn’t a bit out of place.

And Africa, of course, gets the star treatment. Filming in the streets of Kenya, Meirelles allows the juxtaposition of blue and orange (which he developed so gloriously in the Brazilian “Cities of God”) to take on new meaning. Life and light pulse through crowded markets and corner gatherings; AIDS has not yet killed this vivacious community.

In contrast to the candy colors of the Kenyan shanty towns, Meirelles’s London is tinted with the chloroform green of a coroner’s office. Even the displaced Londoners living in Africa carry a certain sickly air around them. They go about their business, even serious business, barely registering emotion.

It would be easy to write off the limp, colorless bigots as the ultimate evil. But “The Constant Gardener” is not quite so predictable; it keeps away from Tessa’s liberal anger at the big “bad guys,” instead focusing its fury on a much more interesting target: apathy. While Weisz’s character embodies the annoyingly over-sincere street-volunteer from Amnesty International (who we ignore on the way back from lunch), it is everyman Justin’s failure that delivers the unique message of the film.

During all of her fact-hunting he sits idly by, showing little interest in anything but gardening, his hobby and passion. Only when Tessa is killed does Justin stop pruning to find out what she was working on — which is, of course, too late.

Betrayed by indifference, Tessa is dead and Africa suffers on.

“The Constant Gardener” expertly runs through the familiar spy paces. There is a particularly good car chase scene through the desert, the requisite backstabbing and a passport-swap a la “The Bourne Identity.” Nevertheless, the heart of this film is a fearless indictment of our culture and moral values. Can it be that it takes no less than the death of a loved one to shake us out of our apathy?

After all the credits have rolled, “The Constant Gardener” ends with a whip crack: “This is a film dedicated to all the AIDS workers who lived and died giving a damn.”

I pay my respects to movie that really does.