After the success of Titanic, a rumour spread online that Leonardo DiCaprio is an alien. Jang Joon-hwan, the director of the 2003 Korean sci-fi comedy Save the Green Planet!, claimed that his script was inspired by Misery and a blog post describing DiCaprio as an extraterrestrial sent to Earth in order to seduce the planet’s female population.

The American actors Jesse Plemons and Emma Stone, aged respectively 37 and 36, are hearing about this internet rumour for the first time when they’re in London’s Corinthia Hotel to discuss Bugonia, an English-language remake of Save the Green Planet! directed by Yorgos Lanthimos from a script by Will Tracy.

“That’s wild,” says Stone. “I didn’t know that.”

“But [DiCaprio] doesn’t have any kids,” says Plemons, comically pausing and leaning in. “That we know of. Maybe he’s got thousands.”

As in Save the Green Planet!, Bugonia concerns a conspiracy theorist kidnapping a CEO in the belief that the latter is an alien plotting to destroy the human population. With long, greasy hair and eyes constantly on the verge of tears, Teddy (Plemons) is a beekeeper who’s assisted by his cousin Don (Aidan Delbis) in tracking down the head of a pharmaceuticals company, Michelle (Stone). Deemed “Leader of the Year” on a Time magazine front cover, Michelle is cold, ruthless, and alienlike as a businesswoman who shudders at the word “diversity”. As Teddy believes aliens communicate through hair follicles, he shaves Michelle’s head. “I loved it,” says Stone, who’s bald for most of the film.

Bugonia spends two hours with Teddy and Michelle in what often feels like a black-box theatre play. Tied up in her home, Michelle is interrogated about her DNA: she insists that she’s human, but can’t prove it, other than her very human screaming. It leads to Michelle yelling, “You’re a loser, and I’m a winner.” It’s arguable that Teddy’s human qualities – he’s weighed down by trauma – have led him here, whereas Michelle’s corporate success derives from ignoring emotions like empathy. However, Stone disagrees.

“In my mind, it’s two people trying to save the world in different ways,” she says. “They both have that instinct to try to better humanity, so to speak, but from different backgrounds.” She laughs at how hard it is to describe the film. “I mean, Michelle’s background isn’t really explored, because it’d be complex.”

“It seems like a very human perspective to me that Michelle would be a CEO who thinks this world has winners and losers,” says Plemons. “It’s cute what you’re doing, Teddy, but you’ll always be a loser.”

Stone nods, adding, “She’s like, ‘That’s fucking life.’”

And the film shows what happens when two opposing people actually sit down to have a conversation: you think they’re insane, they think you’re insane, and it ends in carnage?

“I don’t know,” says Stone. “Everyone has a different perspective from their own specific upbringing, culture, and experiences. It’s hard to write anybody off as insane, because if you knew their whole story from the very beginning, you would probably empathise with their worldview to a certain extent.”

Everyone has a different perspective from their own specific upbringing, culture, and experiences. It’s hard to write anybody off as insane

The remake came from one of the film’s producers Ari Aster – he once cited Save the Green Planet! as the key inspiration for the ending of Midsommar – asking Tracy, an American writer on Succession, to pen a gender-swapped version set in America. When Jang, the intended director, had health issues, Aster asked Lanthimos to helm the project. Shot with VistaVision cameras on 35mm, Bugonia is tonally closer to the real-world creepiness of Kinds of Kindness than the ever-shifting lenses of Poor Things and The Favourite.

Bugonia is also more grounded than its zany source material. In Jang’s film, the kidnapper’s assistant is a circus tightrope walker who participates in cartoonish fight sequences; in Bugonia, Don is lonely, autistic, and increasingly sceptical about Teddy’s rants. “You see two characters and slowly all these layers are revealed, and you start being confused about what you believe, and who to root for,” says Lanthimos in a separate interview, alongside Tracy. “Don represents the audience.”

Another newcomer to Lanthimos’s troupe is the comedian Stavros Halkias as a messed-up police officer. Lanthimos says he was “not really” a listener to Halkias’s cult podcast Cum Town; rather, he’s a fan of Halkias’s “exceptional” stand-up and appearances on the sitcom Tires.

While Tracy is the only credited writer, it was reworked to suit Lanthimos’s sensibilities. (Efthimis Filippou, the co-writer of The Lobster and Dogtooth, is thanked in the credits.) In Tracy’s script, Teddy drowns out Michelle’s screams by playing “Good Morning Starshine” from Hair. In postproduction, Lanthimos replaced it with “Basket Case” by Green Day. “The song I chose was too screenwriter-y, on the nose, and literal about an actual conversation between Earth and the stars,” says Tracy. “Yorgos made the right choice.”

One series of haunting images towards the end of Bugonia is brand-new. Conversely, a climactic montage from the 2003 film is absent; instead, Lanthimos shoots it as a monologue that remains on Stone’s manic face. When I bring up the differences, the 52-year-old Greek director claims he can’t remember the Korean version in detail. “I watched the film once after reading Will’s script, to make sure we weren’t just doing the same thing in English,” says Lanthimos. “From then on, I never thought about the original material.”

“I only watched the film once,” says Tracy. “It was before I wrote it.”

Four of Stone’s last five films have been directed by Lanthimos, and the fifth one, Eddington, strongly mirrors Bugonia in plot and theme: what happens when conspiracy theorists take control? I ask if Bugonia demonstrates the bleak reality of what happens if you sit down with your enemy to have a long conversation in person.

“I think you’re correct in that both people, even if you remove the alien subtext, come from a cultural divide that’s hard to bridge,” says Tracy. “They’ve been arguing with a version of that person in their head for years – virtually or remotely. The fun of the film is taking out the virtual element, giving them space, and seeing how that goes. I like to think on a more general human level, it’s not unbridgeable. It certainly is for the two of them.”

Lanthimos, however, is more optimistic about the film’s message, which is quite something considering what happens in The Killing of a Sacred Deer. “If you really listen to the other person, I’m sure you’ll find some things that are correct,” says Lanthimos. “If you can admit that, which is difficult, then it’d be a different conversation. But a lot of people cannot admit that they do see something that makes sense in the other person.”

As for the “Leonardo DiCaprio is a sex alien” conspiracy theory, Lanthimos and Tracy have also never heard of it before. “Conspiracy theories have been co-opted quite cynically by our White House,” says Tracy. “It’s interesting to think automatically that all conspiracy theories are crazy, stupid, or right-wing. But Teddy’s not wrong about everything in this film. He’s been abused by the system. Like him, I don’t feel necessarily connected to a democratic project. I feel somewhat atomised and isolated. I kind of agree with him on some things.”

Bugonia is out in UK cinemas on October 31