T he Constant Gardener, directed by Fernando Meirelles (City of God) and based on the 2000 novel by John le Carré, is that rare film—one with a brain, a heart, and a conscience. Rachel Weisz, best known as the sexy archaeologist of The Mummy and its sequel, gives a searing performance as Tessa Quayle, a crusading activist in fishnet stockings whose commitment to humanity causes her husband, a flower-tending diplomat played by Ralph Fiennes, to doubt her commitment to him. After she's found murdered in a remote part of Kenya, he discovers that what she'd been hiding had been not an affair but an investigation into a conspiracy involving Big Pharma, the British High Commission, and thousands of sick Nairobi slum dwellers. "I love that the love story and the political thriller are intertwined, so that if one didn't work the other wouldn't work," says Weisz. The cast and crew spent nearly two months filming in Kenya, which Weisz describes as "magical," and she says acting opposite Fiennes was a blast: "I love to improvise and he loves to improvise, so it was just a jam session in Africa. Some of the best lines in the film were jazz that came out of his mouth." Weisz's next movie, due out later this year, is The Fountain, in which she and Hugh Jackman play the same pair of lovers in three different settings: Spain in the 16th century, America today, and outer space in the distant future. The director is Weisz's real-life fiancé, Darren Aronofsky. "It was great," Weisz says of working with her future husband. "He met the actress and I met the director, which is something we don't get to see around the house."