**WARNING: Contains spoilers for Eileen**
If you've read Ottessa Moshfegh's 2015 novel Eileen, you'll know that it includes something of a major left turn in its final act – with a key scene completely altering the mood, and even genre, of the entire book.
Given that Moshfegh herself has written the screenplay for the new film adaptation – along with her husband and writing partner Luke Goebel – it's no surprise that that twist has been left intact, with Anne Hathaway's Rebecca delivering the line that instantly changes everything.
Ahead of the film's release, RadioTimes.com spoke to the duo about crafting the big reveal in the script, and how it was a different process for Moshfegh than writing the original novel – which is narrated from the perspective of the title character (played in the film by Thomasin McKenzie).
"I think there's an expectation for Eileen when she enters this different space, and then there's also the expectation of the viewer who is like, 'Well, we think we're going somewhere, but then it turns out that's not where we're going,'" Moshfegh explained.
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"Both literally, and in terms of the dynamic between Eileen and Rebecca."
"But I think, in the novel, she already knows the story, so she's trying to reveal it to the reader bit by bit - and I think that was really what we were focused on in how we lead the viewer through each scene at Mrs Polk's house.
"You know, at what point do we reveal this? At what point does Rebecca say this? Just to keep the tension and suspense going as long as we can, and then deliver something that's sort of an invitation to even more suspense."
She added that she had enjoyed watching the film with audiences, in that it allowed her to observe people's reactions to the big moment in a way that naturally wasn't possible with people reading the book.
"I mean, when you read a book, it could take you, like, several days at least, and this was just a very concentrated hour and a half," she said.
"And the collective shock was palpable. I mean, it was like electric in the air, and then also the feeling when the movie is over. It's just this sort of stunned... what do you do now?"
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Speaking about his observations of the reactions, Goebel added: "People are too upset at the end for it to have not worked as a tonal shift. People may say, 'Well, that wasn't what I expected,' but, like, it's not like people just get up and go, 'OK.' People are upset.
"And it is upsetting – it goes from something where you kind of think you know where you're going and it's this really enjoyable, charismatic Christmassy film, and then it goes to something really serious.
"That's something that deepens the work into something that we wrestle with as human beings. So I think it's a success in terms of the tone changing."
Meanwhile, director William Oldroyd revealed how he wasn't too concerned with navigating a difficult tonal balance caused by the twist due to his own experience when he first read the novel.
"You have to trust the fact that in the book, I totally bought it," he said. "I think if I had read the book and gone, like, that's ludicrous, I'd have had to look about how we engineer it so it doesn't feel so left field. But actually, when I read it in the book, I got chills... I didn't see it coming."
"It's the kind of twist where you can like go back and see all the hints," added McKenzie.