Reiner, best known as Fig in Orange Is the New Black, founded the production company Broad Street Pictures with fellow actor Sarah Megan Thomas (who stars in Equity with Reiner and Breaking Bad's Anna Gunn), specifically to create the film; the pair had been looking for a project to address the much-discussed gender imbalance in Hollywood.

The film stars Gunn as Naomi a high-level investment banker – we're given no backstories here, refreshingly, although it's not hard to figure out – who has already been betrayed. She is about to take a gamble on a Silicon Valley start-up, when she runs into an old college friend (Reiner), who just happens to be a federal agent investigating Naomi's company – and her lover (James Purefoy), a sleazy hedge fund deal-maker. As Naomi tries to salvage her career, she gets caught in a web of corruption.

Equity is not only co-written by Reiner and Thomas with screenwriter Amy Fox, it's also directed by a woman (Meera Menon), and women make up most  of the crew.

"We also had a female production designer, costume designer, second assistant director, assistant editor – it was a lot of women," says Reiner, adding that the energy was "definitely different from other sets I've worked on". "It was awesome."

She was initially hesitant about a financial story, interested as she is in "telling stories that make the world a better place and have a lot of social impact", until a conversation with a friend who consults for Fortune 500 companies about keeping women in the workforce.

"The stories she told me about the inequity, and the statistics – I was like, oh my God, we have to make this movie to help incite change."

She and Thomas interviewed dozens of women – and men – who work in the financial industry, and encountered many of the same stories.

"Naomi's journey is one that we heard too many times; the same with women thinking they needed to hide their pregnancies," she says, referring to Thomas' character in the film. "The film isn't based on a true story, but there are moments in there that are very specifically true."

Several women bankers from the likes of Goldman Sachs and Barclays acted as advisers and some even invested in the film.

Equity could have been a heavy-handed "issue-of-the-week" film, but it's a pacy thriller whose protagonists just happen to be women. It's just that in most Hollywood films about the finance industry women tend to be decorative – even in 1988's Working Girl, ostensibly about a career woman in Wall Street, Melanie Griffiths utters the line: "I have a head for business and a bod for sin."

Ugh.

"Exactly," Reiner laughs. "When we were making our sizzle reel, we played it for laughs – 'she's not a secretary, she's not a hooker, she's not the token woman in the background...' our goal was always to make a real financial thriller and then it's sort of a secret social mission stealth bomb."

Reiner's character is a lesbian, but this is never discussed or made a focal point; it just is. Something she  says was "a very specific choice".

"We don't talk about it at all. That's the way it should be."

The same with the film's ambiguous ending; viewers are not talked down to and instructed as to who we should like. There are facets to all the female leads that are both likeable and not.

Although we may well find out what happens to them if Reiner and Thomas get their spin-off television series off the ground.

"God willing, we'll see that in the next year, and we will explore all those relationships a bit more," she says.

It seems like a positive, if small, step in the ongoing conversation around diversity in Hollywood, where, according to a recent University of Southern California study, women were given only 30.2 per cent of speaking characters in the 100 top-grossing films released between 2007 and 2014.

It is, says Reiner, too early to say. "I'm a fan of not talking about things too much – just doing what I can."

Equity is showing now at The Nova.