She's been called the thinking man's sex symbol but it has taken a while for Hollywood to take full advantage of sultry Rachel Weisz. The Constant Gardener, in which she stars opposite Ralph Fiennes, is certainly destined to raise her profile yet higher.

Through flashbacks we learn about her character, political activist Tessa Quale, and the events that led to her death, which may or may not have been at the hands of the husband she supposedly cheated on (Ralph Fiennes). 'The love story is about how opposites attract,' Weisz says. 'My character is volatile and flighty... but he gives her stability so she feels safe with him immediately'.

You're quite dead through most of this movie, was that strange for you at all?
I love the fact that this is a love story told in flashback and that there are a lot of assumptions that Ralph and the audience make about my character, that are revised as the film goes on. I think that's a beautiful narrative structure.

Is there anybody at all that you based your character on?
All the research was great, but the real inspiration happened in Africa. When I was in Africa, there was a woman there who was an activist. She was a Kenyan who had been living with HIV for the last 12 years and counselled women with HIV in the slums. She was incredibly generous, and allowed me to accompany her on house calls around the shanty town, to visit patients with her. Meeting the people of Africa, that was my inspiration. It's a very hard thing to explain in a nutshell, but I've never seen poverty on that level in my life. It's very extreme, with a very high level of disease, and yet there's a spiritual wealth that these people have, they were so generous and hospitable.

As an actress, how would you like to be remembered?
I really value spontaneity, and being allowed to stray from the text and be free. I like to try new things, and if this love story is believable, I think it's because of that. Their relationship has the kind of banter that lovers have, that is very hard to script. Real life is messy, it's not neat like a script, and there were scenes in the movie where we just kind of took over, we walked around and the camera just followed us, that's a pretty extraordinary situation.

Your character in the movie is deeply political. So what world issues move you most, and if you had the power, what would you do to make the world a better place?
That was my challenge in playing Tessa. I've always been fascinated by people who devote their life to a cause; people who go to India and or Africa, who put their life in jeopardy to do what they believe is right. What I do for a living is completely different. I'm a storyteller, an entertainer, so I'm nothing like my character, but I had a responsibility to do justice by these people. In reality, the main thing that keeps me awake at night is probably the destruction of the planet, humans destroying the planet.

Your next film, The Fountain is out later this year, and word on the street is it will be a big hit. Your boyfriend Darren Aronofsky directed it, how was it working with him?
It's a great film and great love story so it was a wonderful experience and we're both really happy with it. It's set in three time zones: 16th century Spain, present day America, and distant future space. So in that sense it's a science fiction love story. We filmed them as three separate films, but woven in and out. It's very emotional, and very raw, but also very beautiful - just how I like it.