Emily Blunt in "Girl on the Train"

At a certain point in the film adaptation of Paula Hawkins’ novel “Girl on the Train,” Megan (Haley Bennett), a young woman who becomes a subject of endless fascination for both the other characters and the audience, quits her day job as a nanny, daring to suggest to the baby’s mother Anna (Rebecca Ferguson) that there are greater callings in life than childcare, to which Anna quickly snaps back, “No job is more important than raising a child,” tripping off her tongue as if it was a stock line in place of what she’d actually like to say if she weren’t preoccupied with either the expectations of her largely absent husband (Justin Theroux) or society as a whole, leaving her looking somewhat foolish. It’s a questioning of the traditional roles of women that you rarely see in a medium that usually reinforces them, let alone a major Hollywood production of a runaway bestseller, but screenwriter Erin Cressida Wilson has always had a way of saying what others wouldn’t dare.

“It’s such a different language – film and literature – and sometimes you have to be more subtle and sometimes you just have to say it – say the most obvious thing!” says Cressida Wilson, who allows herself a laugh after being slightly surprised by her own boldness. “There are plenty of lines that were created for the film, [including] that one. However, I think it came out of what the book was saying.”

And if there were ever a book that were a perfect fit for Cressida Wilson, it would be “Girl on the Train” in which the thoughts of the three women at its center are often what cut deepest in spite of being wrapped up in a murder mystery. Told largely from the perspective of Rachel (Emily Blunt), a Metro-card wielding alcoholic recovering from a devastating divorce, the film slowly peels back the haze surrounding the death of Megan, whose seemingly idyllic life grabs Rachel’s interest on her morning ride to work, intensifying when she sees her with a man (Edgar Ramirez) other than her boyfriend (Luke Evans). As the only person with this knowledge, she becomes a prime witness once Megan is found dead, and even a suspect since her memory and judgment is clearly clouded by the booze.

Yet as hazy as Rachel might be on the details, Cressida Wilson takes the unique opportunity of a morally ambiguous protagonist to clearly express female desire in such bracing terms that it makes one’s fingers curl around the armrest. For the screenwriter who first made a name for herself with “Secretary” and once described sex “as a language,” this is nothing new. However, armed with the perspectives of three distinctly different women in a film – giving Megan and Anna their due, as well – with a huge built-in audience, Cressida Wilson adds a layer of transgressive thrills to the potboiler, making “Girl on the Train” less a whodunit than a question of what’s been done to them with years of patriarchal society conditioning of who they should be and capturing the precise moment that they rebel against it. With the much anticipated film hitting theaters this week, Cressida Wilson spoke of dealing with her own expectations in adapting a wildly popular pageturner, as well as the tricks on bringing the innermost thoughts out of her characters and the perks of having a female cinematographer on the film.

Emily Blunt in "Girl on the Train"Did this one find you or did you seek it out?

It found me. My agent gave me the manuscript. It hadn’t been published yet and I just fell in love with it immediately. I was amazed at how Paula Hawkins took the subject of voyeurism and longing and loneliness and wrote it in a way that really can appeal to a very popular audience. I worked really hard on a pitch — it was about 22 pages long, and [after] pitching it, I started to work on it. I finished the draft the week that the book came out, so it was before we knew what a sensation it would be. It was very nice that it suddenly shot to number one. Because of that, we almost went straight into production and that was very exciting because I have never been one to write screenplays just to write them or to make money. I want to make films.

With the three different perspectives and the fragmented timeline, it seems like a tricky novel to adapt, but it’s been said you embraced that immediately. Did you see it as naturally cinematic?

I did. [Paula Hawkins] wrote a very cinematic book and the fractured narrative from three very different points of view scared me in a way, but I come from a background in the theater where I’m very accustomed to non-linearity. I actually found the book is incredibly linear while at the same time fractured and I loved that dovetailing of those two ways of writing. I think that all of her incredible details were part of the puzzle and sometimes I call it the Rubik’s cube. You start to move them around until one day — because they’re in a novel and not a film — and you’re working it and working it and working it and suddenly, oh, that’s the film. All the details add up. I decided to keep those three voices, but favor Rachel, [bringing in] the other two voices through dialogue that seems like it’s interior monologue, but we see when we move into the scenes that in fact it’s dialogue.

There’s a great moment like that when Rachel is actually speaking to herself in a bathroom mirror…

Yeah, at first she’s talking to somebody and then she realizes she’s alone…

Rebecca Ferguson and Justin Theroux in "Girl on the Train"Was it freeing to have those kind of moments? You don’t usually have the wherewithal in a film for characters to be so overtly open with their innermost thoughts.

She’s so drunk, she doesn’t even know she’s alone in the room and that was another trick to get the interior monologue out basically. [With] her drunkenness, she’s able to do that in that scene — to be so out of it, she just goes nuts, but it comes out of her speaking to someone else who just leaves the room and has had enough. In the book, you know everything she’s thinking, but in the film, you can’t unless she’s walking around with voiceover all the time, so I had to figure out ways to dramatize what she’s thinking or make decisions when I’m going to hide what she’s thinking while still staying true to the book.

It seemed particularly clever how you framed the film with that opening line where Rachel says, “My husband tells me I have an overactive imagination,” which doesn’t just tell you who you’re placing your trust in to tell the story, but also puts into play the consideration of how men look at women and vice versa. How did that become a starting point?

This film is very much about the female gaze, which is not just on hot guys, but [how] women look at women and [how] they are jealous or they see themselves and they want something there. The train also has a rocking motion, like a mother’s lullaby, and I think that’s very warming for Rachel, so for me, I tried to make the whole film from the gaze of a woman. Gloriously, it was shot by a woman — Charlotte [Bruus Christensen, the cinematographer] who did much of [her own] camerawork. To me, she is a real amazing story of a woman whose children were on set, and she was shooting this film, carrying the camera herself and really embracing the eye of the script and building upon it in a way I thought was quite brilliant.

Edgar Ramirez and Haley Bennett in "Girl on the Train"There’s a beautifully immersive sequence where Megan is speaking to her therapist and describes the feelings she gets from lying, saying “Lying is like a trip.” Since I don’t think that appeared in the book, where did that come from?

Oh yeah. That’s very much me. It came from trying to get to the core of who is this woman? [Megan]’s lying a lot and I was trying to think, when we lie, what feels good about it? You’re not just feeling bad, you’re not just getting away with something, you’re not just guilty, but there’s actually something thrilling about it. You’re creating your own narrative and sometimes if you do it enough, you become that narrative. And I think that’s what she’s up to. I love that character Megan a lot – of course, the film is about Rachel, but Megan was the one that I really felt had a childish, little girl quality that really compelled me.

You also changed the film’s setting from London to upstate New York. Why the move?

I always think of the setting of this film as being on a train rather than being in a country [since] being on a train is being everywhere and nowhere at once. It’s like being inside your own head and your own fantasy and that’s really where this film takes place. All these characters live in their own head, but Rachel in particular does, just like I do all day long with my writing. She’s riding this train and making up stories and longing for these stories to be hers, but really the interesting thing about longing is while it can be painful, it’s also pleasurable. That’s one thing that I found for Rachel’s character that I felt was true was that she finds pleasure and solace and this sort of balm in watching other people’s lives and making up what’s going on in her head. Sometimes it’s much easier to live that way than to get off the train and live life.  The other thing about fantasy is there’s this natural tendency to think, “Well, it’s fantasy. It’s not real. Why don’t you just get real?” And I always think, well, why is it better to live in reality? Maybe it is better to live in fantasy. What’s wrong with that?

“Girl on the Train” opens in wide release on October 7th.