After first reading the script for My Cousin Rachel, based on the iconic Daphe du Maurier novel, Rachel Weisz phoned up writer-director Roger Michell to ask whether her character is guilty or innocent. It was when he told her that even he wasn't sure that she was hooked. "I thought that would be very exciting to explore, and it made me really want to do this project," she says.

Rachel Weisz in My Cousin Rachel

Weisz loves the way the story pushes and pulls the audience. "The process of the whole film will be trying to work out who to trust and who not to trust," she says. "People will think different things of Rachel. The story is equally weighted in both ways. It will divide people, and that's what makes it such an unusual love story, so compelling and haunting. It asks how much you really ever know a person, and can your impressions of someone go completely, devastatingly wrong?"

To play the role, Weisz had to make up her mind about her character's motives. "I decided whether she was good or evil," she admits. "But Roger told me he didn't want to know! So he still doesn't know. But actually what I found with most people that I've spoken to who have seen it, it turns out not to be ambiguous. I've talked to people who think her charm and warmth is a performance and she's not to be trusted. And I've met people who are more in the camp that she's just a woman trying to be independent and free and is a vulnerable victim of gossip and misunderstanding. You can interpret it both ways, which I find delightful."

She particularly enjoyed the exploration of a woman's place in 19th century society. "These rumours are surrounding her because she's different," Weisz explains. "She has different sexual mores from those around her, different views on marriage and being owned. She's independent, and that causes a lot of negative gossip. As it still would, let's face it!"

The Oscar-winning actress has been outspoken about the need for more female filmmakers and more lead roles for women. "It's as if women were some tiny minority," Weisz laughs. "We're half the planet! So it's important that women are the main characters, rather than just stories about a man with some supporting females. But I'm not one for complaining too much, because I don't know how much it helps. I just think that women should do things by example and just get things made and done."

Watch the trailer and a featurette for My Cousin Rachel: