SHE'S played her fair share of English roses and fun sidekicks, but Rosamund Pike is ready to break out of her box.

Tackling the complicated lead in the highly-anticipated Gone Girl adaptation might just prove the perfect move

She sits munching from a fruit plate. She's pregnant with her second child, and apparently has a craving for watermelon. "I'll gun down any questions that contain spoilers," she warns with her mouth full.

She's referring to Gone Girl, the film adaptation of Gillian Flynn's bestselling novel, in which she stars as Amy Dunne.

The character's so complicated that even Pike admits it's hard to talk about her without giving anything away.

Those who've read the book will understand the complexity of Flynn's breathtaking plot twists that sweep the rug from right under the reader, undoing everything you thought you knew about the characters.

And in the hands of David Fincher, acclaimed director of Fight Club, Se7en and House Of Cards, the big screen version magnifies every intrigue into shock and awe.

Pike knew the scale of the task she was taking on, when she signed up to the project. "I was really aware, because it had come to me from so many different angles," explains the 35-year-old. "I'd heard talk about this book from young girls, men, so many different types of people, and the excitement around it is huge.

"Even now, it seems like Gone Girl was the prototype for a whole new generation of books and characters, and Amy is a prototype for a lot of female protagonists."

Here's what we can reveal: Amy Dunne's a rich, high-maintenance housewife, whose marriage to Nick (Ben Affleck) has hit a rough spot. On the day of their fifth anniversary, she goes missing, and Nick becomes the chief suspect in her murder. As their past is slowly revealed, the people around them begin to draw conclusions as to what might have happened, and why.

"Certainly, I've never had a challenge like this, and I've craved to be stretched in the way this character has stretched me," confesses Pike, looking elegant in a simple navy dress that skims her baby bump, her sleek, blond bob immaculate, and bright blue eyes wide with enthusiasm.

"David is interested in tapping all the stuff that hasn't been tapped and saying, 'Come on, let's pull the guts out of you!'

Fincher has said that he'd wanted an actress who was an only child to play the role (Pike is the only child of opera singers Caroline and Julian Pike, and travelled around Europe with them before going to boarding school), and someone as determined as Amy to get exactly what they want.

As part of the audition process, he and Pike would have long, deep conversations over Skype, talking graphically about sexual harassment, rape and other dark subjects that arise in story.

"When we first met, he probably wanted to see whether I had the guts to go there," the actress ponders. "Or whether I was some sort of precious little English flower who didn't want to get my hands dirty. Which of course, is not the case at all," she says firmly.

Pike has not always simply played the English rose. Her breakthrough role came in 2002 as Bond girl Miranda Frost in Die Another Day. She's had comedy roles in Johnny English Reborn and The World's End, and was brilliant as a ditzy socialite in An Education.

But she admits she started wanting to be more than just the sidekick.

Gone Girl is produced by Reese Witherspoon; the Oscar-winning actress who admitted that even she got fed up with not being sent any decent roles - so started her own production company.

"I got an email from Reese the other day," reveals Pike. "Her film, Wild, is getting tremendous acclaim, and she just said how damn lucky we are.

"These roles, like Amy and her character in Wild, don't come along very often.

"She's very humble about it, but she had the foresight and the appetite to go and seek out those roles."

Pike is following suit. "People are very inclined to ask you to do what you've done before, and keep you in your little box. I've started to think, 'How do we keep women as complicated and interesting?'

"They don't all have to be fragile, and they don't have to be motherly and delicate and admirable all the time."

Not that she's averse to playing mothers.

She also stars in the recently released What We Did On Our Holiday, with Billy Connolly and David Tennant, as a mum-of-three.

"I remember distinctly earlier on in my career where I had to play a mother, and I'd meet this little child and he'd look at me very suspiciously as if to say, 'No, you couldn't be my mother'," says the actress, who already has a two-year-old son, Solo, with boyfriend Robie Uniacke.

"Now, they just look and say, 'Of course you can be my mother', and it's really nice."