The strangest thing about watching Napoleon, particularly the scenes between the eponymous French emperor and his first wife, Joséphine de Beauharnais, is that you quickly realize you’re watching a very dark comedy. That’s in part a credit to director Ridley Scott, who brings an absurdist sensibility to the bizarre power dynamics between one of history’s most notorious war commanders and his mercurial empress. But the tone is ultimately sold by the chaotic, boiling chemistry between their portrayers, Joaquin Phoenix and Vanessa Kirby.

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Kirby especially goes in directions you don’t expect. Her performance is impossible to pin down, a marvel of emotional contradictions and compelling resoluteness. In her unyielding stare and poise, it’s easy to understand how she’s slowly driving the world’s most powerful man completely mad. And in the relationship’s more intense, painful, and even traumatic moments, Kirby imbues Joséphine with a subtle empathy, a lifetime of experiences registering across a nervous flicker in the eye.

With Napoleon in theaters this Thanksgiving weekend, the Oscar- and Emmy-nominated Kirby (Pieces of a Woman, The Crown) joined Little Gold Men for an in-depth conversation about building the most enigmatic character of her screen career. Read on or listen below.

Vanity Fair: There’s a fascinating power differential between Napoleon and Joséphine. When you go into a movie called Napoleon, about Napoleon, you’re expecting this epic portrait of this brutal war general, and instead, in your scenes, you get this portrait of this really resolute woman and this very insecure, at times very strange man. How did you approach it?

Vanessa Kirby: We both felt it was one of the most fascinating, contradictory, and complex relationships we’d ever come across. [Laughs] I urge anyone to go in and explore it more. His letters, for example, even as a starting point—it’s unbelievable that you have this, as you say, military general who’s out there on the battlefield, instigating war and conquering land, and then rushing back to his tent to write these letters, which almost feel adolescent in their obsessive-compulsive nature. He wrote to her nearly every day, and she didn’t write him back in the early days at all.

Looking at their decades-long relationship—how dependent they were on each other; codependent, really—we felt the power shifts within it, the need to possess, [less] a maturing and more a fusing with each other and a need. In any relationship where there’s extreme need and there’s something unhealed in them as individuals when they come together, there’s inevitably going to be something that’s naturally volatile.

You’ve talked about the openness you had with Joaquin to let loose and go off from what was on the script. I believe the slap in the movie, for instance, was improvised. How did that dynamic between you as actors develop?

When you go on a journey that you know is going to involve painful things in a psyche to explore, it always reminds me of when you go do a play, and you go do something like A Streetcar Named Desire. By the end of the play, Blanche, as your sister, has been committed to a mental asylum and has slept with your husband, if you were playing Stella. Ben Foster and Gillian Anderson and I did that show in London and in New York, and I remember us having a togetherness in exploring something that’s searingly painful. That togetherness really helps when you’re going to those places. I felt it in a movie that Shia LaBeouf and I did, Pieces of a Woman; we also had that. It’s a sense of knowing that you’re there for each other despite the realms that you have to go to that are uncomfortable and really unpleasant and sometimes very tough.

Is there anything you remember on your end, bringing something into those scenes that came up in the filming of them?

There was a sequence of scenes all set over one night after he throws her out and finds out that she’s had an affair. Our editor just reminded me, “Some of those takes on the sofa were nine minutes long.” I said to her, “Really?” I couldn’t remember what we did, and she said, “Oh, you guys did everything.” She had to find a 20-second scene between them within the parameters of everything that we had shot. I think I screamed in his face. There were lots of tears. Yeah. [Laughs] The relationship never felt like one you could draw on a graph. It fluctuated so much, where he was absolutely obsessed with her and she wasn’t sure about him…so each scene could be played in different ways depending on where they’re at exactly in that moment, both individually and together. We tried to play things in as many different ways as possible, in case there was a journey there that we hadn’t missed out on by the time we came to the end.

I had these moments watching it like, What is she thinking right now?—as Joaquin is doing something particularly bizarre across from you, maybe. I’d imagine that’s pretty fun to play too.

I played a real character before in The Crown, and I’d so loved the research process, and every single thing that I read about [Princess Margaret] all pointed to the same nature of person. Each account I would read, whether it would be some salacious sort of tabloidy-type book about her or someone within the palace who had faithfully written this account of these two princesses, all accumulated to become one whole. Obviously, I had footage and recordings and things of her too, so it was easier in a way.

I thought the same thing would happen with Joséphine, but it was so strange. Every single book I read about her took a completely different angle and often contradicted the one I just read. It was so confusing because I thought, Oh, my God, okay, wait, maybe by the fifth book it will consolidate all those versions I read of her, but it didn’t. She almost lived six lifetimes in one. She was a young girl who grew up on a tiny Caribbean island, very free, grew up eating sugar cane; she lost all her teeth because of it—I did wear a mouth guard in the movie, but because she didn’t smile with her teeth, you don’t really see it. And then she traveled from Martinique and on her own left her family at 16 to marry this total stranger who was an aristocrat, had two children with him, was shut at home, barely left the house. Her husband was beheaded and she watched it, and then she was released and became a fashion icon at the center of women’s liberation and had lots of affairs with many different generals, including [Paul] Barras, who was the head at the time, and then met Napoleon.

Most people would stay the course of who they are and drop off from whatever the next phase was. But she managed, and that taught me that she must be such a master adapter. A master adapter, to me, is able to hide a lot of what they actually think, because otherwise you’d be outed straight away. You wouldn’t be able to shape-shift like that. How do you bury something and make something ephemeral, to navigate or manipulate your internal life, in order to be okay?

It makes me wonder how you found applying that to Ridley’s filming style. He uses a lot of cameras and not a lot of takes. Given what you’re saying about Joséphine, probably any choice would feel like a bit of a leap.

Yeah, so true. And it was tough. I hadn’t worked that quickly before. Sometimes there might be 11 cameras—it’s the most he’ll use—so you might film it once or twice. I love going as many times as possible because you never feel like you quite hit it and there’s always so much to explore, some of which might be no good at all. So it was on the one hand extraordinary because if something really magic happened, all the cameras would capture it and you wouldn’t have to recreate somehow or try and hit something again. But as you say, when you’re playing someone mercurial like that, you just hoped, dear God, that she has enough internal life that you see inside of it. It’s harder to make one specific, bold choice in the moment because you want her to have that energy.

Ridley has given some quotes of late essentially saying sticking to the narrative is not important. I’m paraphrasing here, but what are your feelings on that generally?

On The Crown, we were having these conversations behind closed doors. Peter [Morgan] would say, “Look, I know as much as I possibly can about the facts, but the conversations that happen around those facts we have no idea about.” It’s just one group of people coming together as an alchemy to interpret that. My interpretation of Napoleon is as one actress that happens to be joining one thing about him—of all the many, many, many things that have been written and discussed. When you read a book, a historian offers a different angle on the nature of the man based on so many different factors…. When you read as many books as you can about this man, this incredibly famous man and a counterpoint in Joséphine, like with all the books I read on her, there wasn’t one way of clarifying exactly who they are.

How did you find Ridley as a director?

He’s so brilliant. He’s a master. He is so accomplished that he storyboards everything before. I came on quite late in the process, and so I said, “Ridley, I would love all your storyboards.” And I printed them all out and put them on my wall at home because I wanted to know what he had in his mind and what we had to get inside of. And when somebody puts eight cameras on a scene in a space and it’s a small intimate scene, he’s cutting as he’s going. You’re in such capable, robust hands.

He’s talked a little bit about this longer cut that’s coming to Apple, and there have been some hints about your prominence perhaps in that cut. What do you know there, based on what you’d filmed that wasn’t in the theatrical version?

It’s quite hard to remember actually. [Laughs] There’s so many different ways it can be edited, so I haven’t asked Ridley yet what he’s aiming for. I know that he’s editing at the moment. I’m really interested to see what will be revealed in that version. There were lots of sequences and scenes we filmed that couldn’t make the movie because it was just too long. It spans so many years. So I don’t know what it’s going to be. I’m as much in the dark as you, I think. But there’s definitely Joséphine’s life before meeting Napoleon—we did film long sequences of that.

And that’s stuff that would’ve helped you unlock what we were talking about earlier, in how she became who she became, right?

Totally. Everything that I studied about her informed how she was able to survive. The main word that kept coming up in everything was survivor. I thought, What is the nature of that, and what does that mean for her? And when you read about the things that she was able to navigate and persevere at, I would’ve honestly collapsed on day two and not been able to continue…. Napoleon was meeting someone who had come so close to death and had witnessed death and had even cut her own hair off because she imagined the guillotine taking off her head. That’s a particular kind of person; that is a person that is resilient and has come close to something incredibly frightening and has met it.

This interview has been edited and condensed.