Pictures courtesy of Netflix
The Woman in Cabin 10 is a thriller that boils the murder mystery down to its appealing essentials. There’s a protagonist, a journalist (played by Keira Knightley), haunted by her past. She becomes both emotionally and literally lost at sea aboard a posh yacht surrounded by the uber-rich. Class, per usual with the genre, plays a role – especially once The Woman in Cabin 10 goes overboard and everyone aboard tells Laura “Lo” Blacklock – an enticing twist! – no guest was staying in the titular cabin.
Mystery ensues, the plot thickens, and everyone – even Lo’s ex-boyfriend, a photographer unexpectedly on the boat trip (David Ajala) – is a suspect.
It’s a yarn in the truest sense of the word crafted by screenwriters Joe Schrapnel and Anna Waterhouse. The couple are no strangers to mystery, given they adapted the legendary Agatha Christie and Rebecca, too, for Netflix. Shrapnel and Waterhouse approach thrillers with suitable glee, which is evident in discussing The Woman in Cabin 10 with them.
The screenwriters, also known for Seberg and The Aftermath, recently spoke with What’s On Netflix about penning murder mysteries and creating a rollercoaster with real stakes.
You both need a very detailed outline before you begin writing. For The Woman in Cabin 10, what early questions did the outline need to answer? What problems needed solving?
Anna: Well, this came to us with [director] Simon Stone attached to the project. The first thing was us meeting Simon, and he wanted to take away the idea that she was an unreliable narrator, which exists in the book. There’s a sense that she’s drinking too much. She starts to doubt if she saw a woman go overboard or not.
Simon wanted it to be clear; he wanted her to be our audience, so we know this happened and her job then is to prove it, to work out what happened and stay alive. Obviously, that changes a lot of the way you have to structure the story because it becomes a who-dun-it.
Joe: We sat down [with Simon again] and beat it out over a couple of days.
The Woman in Cabin 10. (L-R) Keira Knightley as Lo and Daniel Ings as Adam in The Woman in Cabin 10. Cr. Parisa Taghizadeh/Netflix © 2025
What was your relationship to the book once you started writing?
Anna: Once we’d agreed what we wanted to achieve, we thought about, okay, we’ve got to take everything in. The book will exist. Everything in the book, everything that Ruth Ware has created has brought us to this point. It’s a bestselling book. People love it. Netflix wanted to make the book, so we can’t betray the book.
But at the same time, we almost have to at this point let the book go in order to have the space to plot the who-dun-it. Because we’re working in film, in a temporal medium. It’s not like a book where you can pick it up and put it down and you’re in the head of a protagonist who can take you all over the place in terms of what they feel and where they’ve been. Memories from the past pop into their head at the right moment. We have a different set of rules in terms of how we tell a story in films.
Since you all wanted a more reliable narrator, given all the changes that require, what qualities did you start with for defining Laura “Lo” Blacklock?
Anna: The first thing we did was really say, “Okay, who is this woman? What’s she been through? What’s brought her here onto this yacht?” And then once we were there, the fun began because then we could really think about how do we create red herrings? How do we create a sense of danger?
We are really designing a ride for the audience. There are certain things that you’re going to need to do – create fear, tension, pressure on the character, all of those things. And so, that’s when we started designing, I guess, the middle act on the boat with a lot of the characters we updated.
How so?
Anna: It’s a contemporary book, but tonally, it’s slightly different from the book. We wanted to have fun with the characters, so we took some liberties there and invented a few new characters. We molded certain characters from the book into slightly different roles.
It really was a process of invention while at the same time trying to make sure that we were doing justice to the DNA in the book and the purpose of the book.
Your version of “Lo” – her questions are always driving the plot forward, almost like a detective story. Did you both find a journalist to be a great protagonist to drive a story?
Joe: They are excellent protagonists. This was the first actual journalist that we’d written. By pure coincidence, one of the producers sent me a clipping. Someone had written a letter to The Guardian, the newspaper that we feature in the film, drawing the connection that my grandfather was, in fact, a Guardian journalist. It was not a conscious lure to the project, but an interesting coincidence.
That’s great.
Joe: In the book, she’s a travel journalist. It’s logical that she’d been sent on this trip. Changing her to an investigative journalist was entirely for the reasons that you’ve described, that she functions like a sleuth in this movie. It tallied more with our sense of Lo, which came from those early conversations with Simon, that she is very sure about what she has seen. She may not be able to understand it, but we wanted to distance her from the already overplayed genre trope of, does she trust herself?
Anna: I don’t know how much we can ruin [about the movie] in this interview.
You’re safe to spoil the film. It’s been out a while, and congratulations on the fact that a lot of people are watching your work.
Anna: Thank you. It’s gratifying. What’s fun about making movies for Netflix is you do get this massive audience if it hits. It’s satisfying to know that you’re reaching lots of people. But that’s another subject.
Joe: As Anna hinted at earlier, in the book, a lot of it’s internal. A lot of it is Lo’s uncertainty. Obviously for a movie, you need your protagonist to be doing things. We had to invent – invent things that would give the audience the feeling of threat and danger that Lo had in the novel. So, being trapped under the pool, working as a sleuth to have to break into the cabin over the side.
Anna: It was logically starting with what would happen. We wanted clues, real clues that there was somebody in that cabin. That’s where we came up with a cigarette idea. It’s plausible to us that this woman, when we know who the woman is and why she’s there, that she would be stressed and chain-smoking secretly in her cabin.
And so, the cigarette butts were a good way for us to just ground Lo’s sense that she’s right. She has to keep going and investigate because she’s got these cigarette butts. Then there’s the hair in the shower – that was an idea we came up with. And that gave us the sequence where, as Joe says, she climbs over the side of the boat. Apart from falling in the pool, that’s the most dangerous moment for her – until the end of the second act.
Another invention was killing her [ex] boyfriend.
That’s a surprising death. How’d you both land at that choice?
Anna: We needed the audience to believe that her life is in danger, that this isn’t just a story of trying to con the audience into thinking there’s peril for her. Actually, there is peril, and we’re going to watch these people kill somebody. That [syringe] jab was meant for her, and it got him and he died. The stakes are raised for her.
We thought that’s a good tool to give us that escalation of stakes and peril as we go into the third act.
And an unfair death is always great.
Anna: We’ve also got this phrase that Joe and I use, which is “dead by third act,” and there’s always a character who’s dead by the third act. Okay, he’s our DBTA.
Joe: It’s a great rule, at risk of sounding too mechanical about it. My favorite version of it is in Misery with Kathy Bates. It’s Richard Farnsworth as this sheriff; he’s dogged and tenacious. He knows something’s up with this crash and throughout the movie, you think, okay, he’s going to do it, he’s going to save Paul (James Caan). He [finally] comes through the door and Annie Wilks (Kathy Bates) kills him. Boom. It’s wonderful.
Anna: Who now? Because you’re putting all your faith in that guy, putting all your faith in him coming to save the day, and then he’s gone. You’re exponentially worse off than you were before, so you’re even more scared for James Caan and his imminent demise.
As Joe says, they are mechanical, but they have to be handled in such a way that it doesn’t feel like you’re plotting by numbers. It was also why we really built that character up and made this in some way about their relationship.
The Woman in Cabin 10. Gugu Mbatha-Raw as Rowan in The Woman in Cabin 10. Cr. Courtesy of Netflix
Even though you don’t want the process to become mechanical, the beauty of thrillers is the clockwork nature of them. Are there any rules of the genre you two value, maybe even want to lean into when you write a thriller like The Woman in Cabin 10?
Anna: Well, we’re currently adapting Ms. Marple. The very best at this is Agatha Christie, and everybody has copied Agatha Christie ever since. I was just looking at this [copy of The Woman in Cabin 10] again, and even on the back, someone says “a rollicking page-turner that reads like Agatha Christie.”
Obviously, Knives Out is overtly homaging Agatha. We have studied her because the first thing we adapted from her was Then There Was None, which hasn’t been made, but it was an amazing experience. I’m sort of going off-piste here in terms of my answer.
Actually, one of my questions was about Agatha Christie, since you’ve adapted her work. She must be an influence when you write a murder mystery.
Anna: Then There Were None is like the best Swiss watch because you read her and you’re just like, oh, this is a good page-turner. But when you try to adapt and inevitably you have to take liberties – you have to drop certain characters, you can’t have all of them, or you have to change the rhythm of something – you start pulling at these threads and the whole thing unravels, and you realize how perfectly this was constructed. I think we’ve learned quite a lot from her in terms of that.
What other lessons in writing thrillers?
Anna: There are obvious ones, like you can’t have a character unless they’re serving a purpose. Everybody has to have guilt cast upon them. Everybody has to be suspicious, and everyone sort of has to have a secret, but it’s probably not the secret you think it is.
I think that’s a helpful rule – if every character can have a secret that they’re not telling somebody, it could be a secret like, I stole your biscuits, and I’m not going to admit it, but it gives them this veneer of guilt. Of course, the audience is going to interpret their guilt in relation to the big crime committed. And then there’s rhythm.
The Woman in Cabin 10. Keira Knightley as Lo in The Woman in Cabin 10. Cr. Parisa Taghizadeh/Netflix © 2025
What rhythm does The Woman in Cabin 10 require? How else do you create that rollercoaster sensation you wanted?
Anna: There aren’t any hard and fast rules about rhythm, but you can feel it when you’re writing. You need scares, you need ramping tension, and you need to make sure you’re keeping the audience on that ride for the whole time.
I always think of this as in terms of rollercoasters – you design it to give the audience these thrills and then suddenly turn in an unexpected direction.
You can read a script back and you think, oh, it’s getting a bit boring, too much exposition right now. Then we need to do something different. It’s instinctive, I think, in that way rather than being prescriptive. There’s no map, but it comes from your sense of what journey the audience is going on and at what point they might need to be surprised.
I think surprise is a big word, and that can go for the way a dialogue turns or anything. I think that’s a good principle to bring to any writing – just be unexpected. But particularly when you’re dealing with a murder mystery or thriller.
Joe: The perfect dramatic form is a joke, isn’t it? Which is just, it leads you one way and then, oh no, it was actually that, and then you get the laugh. In a thriller, you get the shock, or you get the death, or you get the surprise. The best ones are the ones that don’t lead one direction and then it’s behind you.
Rebelling against expectation is what you are aiming for, isn’t it? Rather than, as you say, any hard, fast, concrete rules. I’m instinctively mistrustful of any “this has to happen by page [X]” or something. Those are the rules or principles rather than any sort of packageable blueprint for a screenplay.
Anna: Construction is important, particularly in this genre, but the most important thing is caring about your character. If you don’t care about your character, then it doesn’t matter how many turns and jump scares and reversals you can come up with. It is about making the audience care.
The Woman in Cabin 10 is now streaming on Netflix.
