Can you put a face to the banality of evil? How about two? On a bright London morning, Sandra Hüller and Christian Friedel are back from having their picture taken. The German actors are here to discuss The Zone of Interest, the film they have made with the director Jonathan Glazer (Under the Skin), loosely inspired by Martin Amis’s 2014 novel of the same name. But for a moment, we talk instead about Friedel’s liking for porridge; how Hüller, by contrast, doesn’t eat this early. And they smile and pause, aware of what comes next.

In The Zone of Interest, Hüller and Friedel play a couple exhumed from history: Hedwig and Rudolf Höss, who, during the second world war, raised five children in a sturdy villa with a pretty flower garden. It stood over a wall from the death camp at Auschwitz, where Rudolf was commandant. So the chit-chat ends.

The pair are dressed for the photograph: Friedel, 44, cherubic in a polo neck, Hüller, 45, self-contained in black, a veteran of the circuit since her recent bravura performance as a writer accused of murder in the thriller Anatomy of a Fall. “I try to flow through it like water,” she says of the attention. “Like Bruce Lee.”

Both are brilliant in a film that would overwhelm most actors. On screen, we never see the gas chambers or anything else of the camp, although we always hear it. Instead, Rudolf frets about the state of his career and Hedwig tends the azaleas.

Hüller didn’t want to play her, she says. When approached, she recoiled. She had seen too many German actors dressed as Nazis in banal period dramas. “Also I feel no urge to investigate this sort of character. Cruelty and violence don’t interest me.”

As heard in Anatomy of a Fall, Hüller speaks fluent English. Friedel is more hesitant. His voice is gentle. He says later he has never drunk alcohol “or taken a drug”. His first film was Michael Haneke’s The White Ribbon, set before the first world war. Casting him as a kindly teacher, Haneke told him he had a “historical face”. He first met Glazer and the producer Jim Wilson in London in 2019. He felt daunted by the film they described, but compelled, too.

“Even in kindergarten, I loved to bring ideas to life for others with singing, dancing, hand puppets. This was part of that same journey. Even though the idea is unbearable – a killer of millions who plays catch with his children.” He asked if they had yet cast Hedwig. “Because it had to be someone so good, but who wouldn’t think” – he gives a diva-ish flourish: “‘Here I will do something spectacular.’ So I said: ‘Do you want Sandra?’”

“You never told me this,” Hüller says. “How sweet.”

The pair first met in 2013, acting together in the deadpan 19th-century romance Amour Fou. They stayed friends. They had much in common. Both grew up in the former East Germany: Hüller in small town Freidrichroda, Friedel in Magdeburg. As adults, each embraced the rigour of German theatre. (Both still perform on stage.) They are also talented singers. Friedel fronts art-rock band Woods of Birnam; 2016 absurdist comedy Toni Erdmann gave us Hüller’s remarkable version of Whitney Houston’s The Greatest Love of All.

And yet. “They’re so different, aren’t they?” Wilson says. “Christian is pure sweetness. Unmediated. And Sandra is complex. She can be so funny, but she roils with inner life.” Despite Hüller’s reluctance, Wilson says there was no real Plan B if she or Friedel passed. They were the only actors he or Glazer wanted.

Hüller changed her mind on learning what the film wouldn’t be. “Meeting Jonathan, I realised it wasn’t actually about the Hösses. It was about people ignoring terrible things right where they live. A film to make us unsafe in the cinema. As we should be. We should ask: is this also us? Do we do this, too? Do we do this every single day?” Hüller’s speech has taken on the pulse of a monologue. “So yeah,” she says, abruptly. “This made it interesting.”

I say the film made me confront the Holocaust and other inhumanities: even the climate crisis. “My daughter told me she doesn’t want children because the world is dying,” Hüller says. (She is the mother of a 12-year-old.) How did she reply? “I said I took her seriously, though her age means it is not a decision for now. But there is smartness in her thought. Even a certain beauty. Maybe it should all fall apart.” Friedel looks a little sad.

The Zone of Interest was filmed during the summer of 2021. Preparation was not so different from any historical drama; Friedel learned to ride horses. But the location underscored the movie’s singularity: not the Höss villa, now decrepit, but another house on the Auschwitz site that also adjoined the camp.

Inside, 10 hidden cameras filled the building in lieu of a crew, so Friedel and Hüller could perform without the artifice of film-making. (Glazer has called the setup “Big Brother in a Nazi house.”) Creatively, they say it was fascinating.

It was also hard. Some pressures were professional; others personal. The abyss gazed back. “There was a cocktail of darkness,” Friedel says. “We were so close to the camp. We felt responsibility to the victims. My subconscious rose up.” He suffered nightmares. The Friedel who Hüller says “just cannot be an asshole” strove to find inside himself a man who could administer the Holocaust.

Hüller was tested, too. On Anatomy of a Fall, she implored the director Justine Triet to tell her if her character was guilty. Historical evidence makes clear Hedwig Höss knew exactly what was happening beyond her garden. Usually, Hüller builds her characters from empathy. “But I gave her nothing.” Hedwig, she believes, never looked inward herself. You sense this is among the worst things Hüller could say of anyone.

The shoot, they say, was “lonely” and “uncomfortable”. Friedel watched Money Heist for distraction. Each evening, he and Hüller ate together. “It was important to have a colleague.” That winter, however, he shot further scenes without her. “I was in that uniform again, and now it was just me.” He broke down in tears.

I ask how they felt finishing the shoot. Disappointed to end a unique exploration? “I was so happy it was over,” Friedel says. Actually, he beams.

Hüller nods. “And I’d love to work with Jonathan again, in 15 years.” Only joking. Sort of.

But nothing is over, really. There are still the interviews. For Hüller, the spotlight has already been cranked by Anatomy of a Fall: Vanity Fair snapped her in Los Angeles in lilac Prada. The next time we meet is over video call. She is back home in Leipzig, where she lives with her daughter and a dog. Now she wears a baggy T-shirt that says, from what I can see: God Loves Me.

Awards buzz surrounds both her recent performances. I think of her at film industry parties and recall her remark about channelling Bruce Lee.

“I can own the conversation at a party. I can talk about whatever I like. But no, it doesn’t feel like home. And it shouldn’t. It’s work. Like now. My ego is flattered you want to know about me, but soon you will want to know about another person.”

Yet work and life can blur for actors. Despite her revulsion at Hedwig, Hüller’s dog doubles as the family pet in The Zone of Interest. And the credits of Anatomy of a Fall featured her own teenage years, glimpsed in personal photographs. Triet, she says, first asked for them as detail for set dressing. Hüller only learned the plan had changed much later.

“So it was a shock. But I love Justine, and I’m fine with it.” And she makes a face that makes me laugh. “Anyway, it is important to accept your 14-year-old self.”

She talks about her routine in Leipzig: time spent with her daughter, and time alone. She speaks highly of both. She enjoys the city’s energy; likes watching people in supermarkets. She says she was able to shake off the Hösses, but the shoot stayed with her: a reminder of German “ancestral guilt”. She was moved, too, by the kindness of staff at the Auschwitz site, and that of the wider local community.

I wonder out loud about her T-shirt. God loves me? She bursts out laughing, then reads the slogan in full: “God Loves Me – And There Is Nothing I Can Do About It.” She stands to show me the rest. A teddy bear stares out, stuck in a hideous Halloween pumpkin. “Yes. I saw this T-shirt on the internet. And I found it very funny. So I bought it.” She is still laughing when she sits back down. She might also be blushing.

Friedel is also in Germany when we speak again, at home in Dresden. He was up late rehearsing with his band. No drink or drugs, of course. “No, my drug is ice-cream. Less dangerous for my mind. Just my body.”

He admits he is still haunted by The Zone of Interest. “The emptiness hasn’t left me completely. I still need time to check it out of myself.” He tells me now he had a panic attack while shooting. But he likes to discuss the film, he says. “It helps.”

He has found others keen to talk about it, too. One was the actor Josh O’Connor, who met him after seeing the movie, failed to recognise him and urged him to see it. Inevitably, after screenings, there have also been questions about Israel and Gaza. “It makes me even more aware the film is about right now,” Friedel says. “The message is timeless and universal. A darkness is inside us all. And history repeats.”

The film comes out in Germany next month. Hüller is curious to see the response. Across the country, the far-right Alternative für Deutschland are having startling electoral success.

“They are a fascist party. We should just say fascist. And now fascists no longer encourage Germans to simply forget the past. They justify it. They say, again, ‘It is good to clean this country up.’ So the rest of us must talk of humanity instead.”

To Hüller, you sometimes simply draw a line. In Leipzig, she tells me, she was walking her dog when three boys of about 17 began shouting insults. Had they recognised her? She smiles. “Nooo. Anyway, I showed them the middle finger. Because I thought: ‘This is not how you talk to me.’” Her manner is tickled now. “They told me to – well, let’s say, they cursed at me. Then they threw something! And then they said something bad about my mother. Who they don’t even know! So I laughed at them. I thought: ‘Do you really think this is how you walk through the world? Well. You will not.’”

She makes it sound simple. Was she not scared things might turn violent? She grins. “Oh yeah. But I just thought: ‘No. Their way is not going to work.’ And I had a moment of faith it would all turn out good.”

• The Zone of Interest is in UK cinemas from 2 February and Australian cinemas from 22 February