But take us back to Joséphine’s drawing room, where dom-versus-dom dynamics result in a showdown that could have filled several seasons of reality TV, with Kirby’s purr often carrying the day. She gets the film’s final word, haunting Napoleon from beyond the grave, just as she reportedly colonized his last gasp on his deathbed.

Kirby’s Joséphine joins the sisterhood of director Ridley Scott’s women, characters marked by strength and savvy, overtly in “Thelma & Louise” and “G.I. Jane,” but just as palpably in scene-stealing turns from Lorraine Bracco in 1987’s “Someone to Watch Over Me,” Jodie Comer in “The Last Duel” and Lady Gaga in the deep-dish-of-crazy “House of Gucci.” Though his choice in scripts can sometimes be suspect, Scott may be the movies’ most consistent stealth feminist.

“Ripley was such a reference for me,” Kirby says via video call of Scott’s most iconic female creation, brought to life by Sigourney Weaver in the 1979 classic “Alien.” Clad in black and in a thoughtful mood, Kirby is game to indulge my pet theory — up to a point.

“The film didn’t signal endlessly that she was a woman,” she says. “She was just a human. She happened to be female. And I think that, to me, is what radical female filmmaking should do. I would much rather it be less gendered. I want to play a human being that men can relate to because it’s a human experience that she’s going through, and that feels like the next frontier of filmmaking we need to get more of.”

Vanessa Kirby, photographed at Corinthia London in 2021.

(Matthew Lloyd / For The Times)

Aside from her mischievous flashes in the “Mission: Impossible” films, the Wimbledon-born Kirby, 35, is best known for her two-season turn as a decidedly human Princess Margaret in “The Crown,” composed of equal parts flintiness and heartache. To Kirby, it’s these “messy, contradictory, anti-heroine-type parts” (she mentions Gena Rowlands’ work with John Cassavetes) that inspire her. It’s also what drew her to Joséphine.

“There must have been something inherently unknowable about her, something that he couldn’t possess,” Kirby offers as a window into Napoleon’s obsession with the ex-courtesan (especially visible in Joaquin Phoenix’s humorous take, bordering on adolescent frustration). “He could go and conquer all these lands but he couldn’t hold her. She had to navigate an extremely difficult world to survive. And he could never own her.”

Much of that enigmatic quality comes through in “Napoleon’s” wordless passages, touching on Joséphine’s internal craftiness and then, later, her loneliness. These windswept moments are unlike any in Scott’s career, suggestive of an entirely different Austen-like narrative unfolding off-camera. Scott, per his nature, has teased a director’s cut, one that’s an hour-and-a-half longer and Kirby-heavy.

“A brilliant listener,” says Scott, 85, calling from London, of Kirby. “I love Vanessa because the relationship, while never aggressive, is always fun. She’s full of ideas, which I love.”

Vanessa Kirby in the movie “Napoleon.”

(Aidan Monaghan / Sony Pictures Entertainment)

He wouldn’t call it coyness but rather a type of creativity. “I’m attracted to that kind of woman who says what she thinks,” Scott says. For the record, he can roll with being called a feminist (“absolutely”), which he tracks back to his mother, the “dominating force” in a domestic situation in which his father, a career military officer, was always away. “He was a sweetheart,” Scott says. “My mum was always the boss.”

Kirby, meanwhile, has her own reasons for those tip-lipped smiles.

“She used to suck sugarcane as a child and lost most of her teeth,” the actor says, relating an insight into the Caribbean-born Joséphine that doesn’t even get mentioned in the film. “I mean, notoriously bad teeth, which meant that she never smiled with her teeth, but she was very playful by all accounts. So she did smile a lot. I actually wore a mouth guard with rotting teeth, but in the end, those scenes weren’t in it.”

Her deep-dive prep into the voluminous scholarship on Joséphine — much of which “didn’t add up,” in Kirby’s view, a clue to her mercurial nature — came late during the pre-production after Comer left the role because of a scheduling conflict. (The 61-day shoot needed to move earlier.) Kirby seized on physicality to get to an interior place, an instinct that served her well during her early, celebrated years on stage doing Isben, Chekhov and even a Stella Kowalski in “A Streetcar Named Desire.”

It also suited Scott’s shooting style: long takes, not a lot of notes, multiple cameras and a prankish sense of humor. Legendary for catching his actors off-guard since springing the famous “chestbuster” scene on an unknowing cast in “Alien,” Scott had a surprise in store for Kirby, aided by a playful Phoenix.

“We didn’t tell her in that breakfast scene that he was going to say, ‘I want to make a baby now,’ and crawl down under the table,” says Scott. “She didn’t know that was going to happen. I said, ‘Whatever happens, just keep going.’”

“I think that’s why I laughed!” Kirby says, smiling at the memory. Another scene, one of the most mesmerizing in “Napoleon,” is a lengthy sofa snit-turned-seduction that she recalls was captured in nine-minute-long takes.

“It’s crazy, the amount we had to shoot,” Kirby says. “We did everything in that scene. I mean, we were screaming each other, we were kissing. There was so much in that scene, and I couldn’t remember those nine minutes.”

Vanessa Kirby and Joaquin Phoenix in the movie “Napoleon.”

(Aidan Monaghan / Sony Pictures Entertainment)

Kirby is just about to shoot “Eden,” a Galápagos Islands-set survival thriller with Ana de Armas and Sydney Sweeney, directed by Ron Howard. Marvelites are pre-freaking out over rumors of her doing a Sue Storm in a new “Fantastic Four.” (As if Kirby could ever play an invisible woman.) Bigness, you sense, is coming for her. It’s a pivot her fans may want to stave off for a few more films. Unless, of course, she can reunite with Scott, who knows how to wear it lightly. “I’m asking him all the time,” Kirby admits.

For now, though, there’s the oasis she created with Phoenix, which sounds like the work she really wants to do. “We knew we had to create something that was unusual and not conventional because they weren’t at all,” Kirby says, noting that both Napoleon and Joséphine were outsiders who rose and fell in Parisian society together.

“It was almost like a recognition of: I see you, I know you,” she says. “We wanted their first meeting to have that kind of strange knowingness between them that’s almost incomparable: My essence understands yours in the most unlikely of ways. And we will always be drawn to each other.”

She’s articulate about how she does them, but there’s a mystery to Kirby’s best performances, an in-joke only she gets. Let’s hope her Joséphine sticks around for a while.