The big question I want to ask Elizabeth Banks is a simple one: How on earth did a small-budget Kiwi film land an A-list Hollywood star like her?

When A Mistake appeared in the programme for this year’s New Zealand International Film Festival, I assumed there’d been a mistake. That in the deadline rush the wrong photo had been used or the film had been mislabelled and ended up in the local film category in error.

Further reading revealed that no, all was as it should be. Elizabeth Banks was indeed starring in a small New Zealand medical drama about a doctor who makes a fatal error during a routine surgery and the harrowing fallout from that mistake.

Elizabeth Banks and Rena Owen star in a New Zealand medical drama about a doctor who makes a fatal error during surgery.

When we connect, Banks is back in Los Angeles and on her way home from a day shooting her next project.

"I’m great," she smiles before her screen goes black and she says, "I’m going to keep my video off because I’m in a car driving. Well, I’m not technically driving, someone is driving me, but I still am going to keep my video off."

At that moment I should have turned my screen off as well. But as I was sitting in my stationary office and not in a moving car, I didn’t.

So, looking at the black screen where her smiling face had been only moments before, I cut straight to the chase and ask: "How on earth did a small-budget Kiwi film land an A-list Hollywood star like you?"

The answer is fairly dull. Banks says the script came to her via the "typical agency route". But what she says next is anything but.

"I read it and loved the writing," she says. "At the time, the character was British. I said, ‘Is it okay if I play her as a New Zealander?’ It felt the most correct to me in terms of who actually works in the healthcare system there."

Kiwi Rena Owen plays a grieving parent.

As well as her artistic reasoning, there was also another, more sneaky, reason behind Banks’ request.

"Frankly, I felt being surrounded by the New Zealand accent would make it really hard to do a British accent," she laughs. "I thought if the character’s a New Zealander, then every day when I go get coffee I can just try and use the accent and keep practising."

Many great actors have struggled with our accent. There’s a nuance to it that’s tricky to pin down.

"I felt that!" she says. "I was very – and I’m still – afraid of people seeing the movie and judging the accent. It’s terrifying."

To get it right she would record her scenes and then send voice memos to her dialect coach asking how to improve her pronunciation. "I worked really hard."

In A Mistake, Banks plays Dr Elizabeth Taylor, a gifted surgeon whose patient survives a mistake on the operating table but dies a few hours later in intensive care. The investigation into the tragedy takes on a life of its own when the media gets involved and quickly spirals out of control, sending her into an extremely dark place.

The film is unrelentingly bleak and shot in a colour palette that’s had the life sucked out of it. It is heavy, compelling viewing.

"I thought what Beth goes through was really intense and interesting. I kept asking myself, ‘What is the mistake?’" she says. The film keeps this hazy. There’s the mistake in the operating room, but there are a handful of others, including the behaviour afterwards, the way the investigation is carried out, and the actions of the dead patient’s parents, to name a few contenders.

Banks' performance is powerful and emotionally complex.

"There were so many interesting ideas in the script. I thought it was deep and something we could deep-dive into," she says. "And really get our teeth into."

At the crux of the film, which is based on the novel of the same name by Wellington author Carl Shuker, is Taylor’s fraught relationship with the hospital’s management, which, despite her being its best surgeon, is prepared to hang her out to dry as a scapegoat.

"I’ve certainly been a woman in a man’s world in my life," Banks says. "Especially when I direct films. I feel like I’m somebody who’s in a position with a little bit of power but there are often times where I have felt undermined in that position, despite my power. That for me was a connection point to her."

It’s hard to picture anyone disrespecting or undermining Banks. Talking with her, she is assertive and confident. She’s professional, friendly and genuinely respectful when answering my questions honestly and candidly. Surprised by her revelation, I ask how she dealt with those moments.

"I tend to constantly just try to lead by example and remain as kind as possible, even in the face of idiocy, because love and kindness will always win out. And mostly people, you know, they just need to be supported," she says, giving a very lovey-dovey answer.

But then she says, "But there are some people who are just hopeless.

"I stopped trying to please everybody. I stopped. I don’t need to be friends with everybody. I want to have mutual respect with people. That’s the most important thing. And certainly in a job situation where there’s pressure to get something done – and especially when you’re making art – you need to have a lot of faith in your fellow collaborators.

"Once that’s gone, if that’s eroded in any way, I typically am like, ‘This is not going to work out.’ I decided that practicality and being true to my feelings typically lends itself to the best results. Otherwise, you’re just resentful and angry."

The film's colour palette is intentionally subdued.

No such problems on the set of A Mistake. She says she loved working with the local crew. She filmed in and around Auckland for about eight weeks, managing to keep a low profile. For the first few weeks, her family were here and they’d often catch the Devonport ferry to explore the city.

"We had a lot of fun dinners, had a lot of good food and explored the amazing beaches. One of my favourite things about Auckland was what a walkable, wonderful city it is with so many great neighbourhoods to go to."

Most evenings after filming wrapped, she’d walk down to the waterfront or through the nearby neighbourhoods. These long walks were a way to distance herself from the relentlessly grim situation of her character and the brutal, overpoweringly bleak vibe of the film.

You are not eased into it. The opening sequence in the operating theatre is gruesome, with exposed organs and blood gushing everywhere. It puts you right in the heart of the events and is not for the squeamish.

"I’m really proud of that stuff," Banks says, joy apparent in her voice. "I worked so hard to learn how to sew in surgery. I worked with a surgeon in Los Angeles – he’s the main consultant on Grey’s Anatomy – and did tons of work on surgery and suturing. We all worked really hard to make that look as realistic as possible. I feel like I could sew someone up. Not maybe inside their heart, but I could certainly sew somebody who had a cut. I’m definitely not squeamish about how to tie it up."

Banks plays Dr Elizabeth Taylor, a gifted surgeon.

Banks carries A Mistake. Her performance is powerful and emotionally complex, her Kiwi accent passable. Critics have called the film a "provocative and engrossing psychological character study" and "an intelligent adult drama".

The success of the whole movie rests on her believability and investment in her character. She said she did not feel that pressure. "That’s what I live for.

"Honestly, I feel like I didn’t have opportunities to play the lead role in films until very recently. And now I’m taking as many of those opportunities as I can.

"I was relegated to a lot of secondary roles and supporting cast, especially in a lot of the movies I made with amazing leading men. I don’t begrudge any of those experiences, but I always knew there was a leading lady living inside me. And I’m thrilled to be showing her off right now."

Then she pauses for a second. I can’t see her but I can picture her, sitting in the back seat of the car, being driven through the glitzy streets of Los Angeles, talking to an entertainment writer on the other side of the world about her latest leading role.

Then she continues, saying, "I’m feeling like I’m living in my power at 50 years old in a way that I never have before. I truly love it."

A Mistake is in cinemas nationwide.

Karl Puschmann is an entertainment columnist for the Herald. His fascination lies in finding out what drives and inspires creative people.