You could say that the director Martin McDonagh has found his niche. His latest film, Wild Horse Nine – the follow-up to 2022’s award-winning The Banshees Of Inisherin – centres on two squabbling middle-aged men on a remote island. Only here, swap Colin Farrell and Brendan Gleeson on a fictional oileán during the Irish Civil War for Sam Rockwell and John Malkovich on the real Rapa Nui (Easter Island) just before Chile’s 1973 CIA-backed coup d’etat. (And a donkey for a horse.)

“I can’t remember if there were rumours flying around that he was going to do another movie with two more bickering men on [an] island,” says Eimer Ní Mhaoldomhnaigh, the costume designer who worked with McDonagh on both films. “The hope is always there that you will get to work with somebody again. So, it was a real treat to pick up from, not exactly from where we left off, but, you know, to keep that relationship going. When you work with somebody a second or a third time, there is a little bit of a shorthand there.”

In Wild Horse Nine, Rockwell and Malkovich play Lee Chesterfield and Chris Carlisle, two CIA operatives embedded in Santiago during the brief administration of President Salvador Allende, Latin America’s first democratically elected socialist leader. We say embedded, but with Ní Mhaoldomhnaigh’s help, they stand out – much like the moai (“big heads”) on Rapa Nui.

“There’s no build up,” she says. “They have to be recognisable from day one as what they are.”

She calls it “hiding in plain sight” – at one point, Chris (Malkovich) goes as far as saying the quiet part out loud, telling two students that they do, in fact, work for the CIA. “It’s a bit like Richard E Grant on The Traitors, saying, ‘I’m a traitor’. And everybody’s going, ‘What? You’re not supposed to say that’,” Ní Mhaoldomhnaigh says.

Rockwell’s character is clearly American, Ní Mhaoldomhnaigh notes. “When he’s in Santiago and he’s photographing students outside the church, he’s pretending he’s a tourist.” As part of his cover, she put him in western clothing of the era.

“Lee has a swagger and a confidence, a 1970s cowboy in a suit,” she says. “His look is definitely embedded in the 1970s vibe, and the colours are strong and contrasting. I also loved using knits for Lee. Sam has a great figure – he can really strut the 1970s look: flared pants, a fitted top or shirt tucked into his pants, a silver buckle, a Cuban heel. Sometimes a leather jacket and jeans, sometimes a suit. His look is strong, unwavering and independent, just like Lee. He has it all.”

His partner, meanwhile, has been stationed in Europe for decades previously and has a worldly – and world weary – flavour to him. “Chris is a bit more ‘old guy in crumpled suit’, slightly too big for him, that you kind of walk past, even with the shirts in bright colours.”

She says that Malkovich’s character will “wear and do what he wants. Nobody will dictate to him. He is not a slave to fashion – and his suits can and are a bit dated. Also, he is ill, and being ill, I wanted his suits to be a little ill-fitting and to look a little tired and care worn. By contrast, there is a dapperness to his shirts and ties, and always a certain care or planning as to how he puts himself together. He is always dressing for the occasion in his own way.

“The viewer never quite knows what he is thinking or planning next. I wanted that element of surprise in his shirts and ties, a bit of mischief that disguises a hard reality. There is always an air of mystery to him.”

Ní Mhaoldomhnaigh describes Malkovich, fittingly, as “a clothes horse”. “He would talk to you all day about clothes,” she says. “He’d talk about the facing in a jacket and buttonholes. Not in a boring way. He loves clothes – he had his own fashion line – and he’ll talk about fabrics and manufacturers and who’s good at what and which country is good, to get shirts made.”

She says this is not a conversation you’d usually be having with an actor. “The costume is part of the character. It has to be correct. But, you know, John… I suppose he’s very intellectual. He loves the history of clothing. Who invented the zip and why.”

The vivid tones, patterns and textures of the early 1970s are key to the film’s wardrobe. “The good thing about having done Banshees was that I knew Martin was not averse to colour,” Ní Mhaoldomhnaigh says. “Sometimes, directors can feel, ‘Oh God, it’s too much,’ or ‘It’s too busy – it’s going to take away from whatever’s going on’.”

And also the materials. “You have to use the fabrics from the period to get the drape and flow and the fit. I have a lot of contacts so I used all of those and shopped everywhere and anywhere. Vintage shops, online, market dealers, vintage fairs. It was a lot of fun and a lot of leg work.”

Unlike his onscreen characters, McDonagh himself is far from belligerent, Ní Mhaoldomhnaigh reports. “He’s really collaborative, but he’d also tell you if he didn’t like something – and that’s really useful. And if he’s not sure, that’s kind of fun, too. You have to win him over. I was just throwing stuff at him. Visuals and references and fabric swatches and colour, you know. Mood boards.

“With a film like this you have to dig deep with the research,” she says. Here, she drew from her experience working on the likes of The Wind That Shakes The Barley and 2008’s Brideshead Revisited. “Social history is always very important with a period piece. How did people live? Their social status, the politics of the time all feeds in to how people dress and you need to have an understanding of that to make the costumes come alive.”

The military garbs in the film are “very good reproductions of the uniforms of the time”. However, she found sourcing civilian clothes and fabrics from the early 1970s challenging while in Chile.

“Maybe they’ve been erasing them,” she says. “I don’t want to read into it too much, but you wonder what’s going on here.” Following the coup, much evidence of this era was wiped out in Chile, along with left-wing, progressive and indigenous voices, during the “cultural blackout” of Augusto Pinochet’s military dictatorship.

“When I went to Santiago during early prep, I visited the Museum of Memory and Human Rights, which is very moving and devastating at the same time,” Ní Mhaoldomhnaigh says. “I wanted everything to be very faithful to the time, to honour the people who lived through and those who died during that dreadful epoch.”

The film deftly touches on real historical events. But the characters are gloriously exaggerated, as vivid as the colours they wear. “Martin’s films are always a little bit heightened,” Ní Mhaoldomhnaigh says. “With Banshees, people said: ‘People didn’t dress like that’. But it’s a fable. It’s not a reality, you know?”