‘When I see season one I think: who is that child?’ – Industry star Myha’la on making TV’s biggest sleeper hit

On a video call from her New York apartment, Myha'la looks sufficiently ready for business in an all-black outfit, undersized glasses pushed down the bridge of her nose and the cityscape outside dominating the frame. It's fitting: we're here to discuss the return of Industry, the hit BBC/HBO series she stars in, which is set in a merciless London financial centre recreated in a Cardiff studio.

Over the past two seasons , we've delved into the deeply stressful environment of fictional investment company Pierpoint & Co, based on writers Mickey Down and Konrad Kay's own experiences as overburdened finance grads. It's a world where your colleagues are more likely to offer you a line of coke than a cup of tea, and where Myha'la's character Harper Stern uses her talent for bending the truth with aplomb. But if you look just below the surface, you'll find horrors of all kinds; in the opening episode of season one, one of Pierpoint's overworked and undervalued graduates dies in the office toilets.

"If someone was like: do you have sympathy for people on Wall Street or whatever, I would generally be like ... no," she says. "But when you see some of the things these people have gone through, it does help you empathise."

Industry is centred on all-or-nothing relationships that fly in the face of professionalism. At first, Harper, a Black American woman, is firmly under the wing of Asian American Eric – even after he finds out that his self-assured protege is a college dropout who lied her way into their distinguished firm. Eventually, she is forced to give up her position, lest her insider trading with Jesse Bloom (last season's guest star Jay Duplass) land her in even deeper trouble. Harper's relationship with Yasmin (Marisa Abela), a troubled nepo baby trying to distance herself from her toxic father Charles, is a warped sisterhood – not least in season three, when Charles is missing, presumed to have gone on the run amid fraud allegations, and Yasmin is being stalked by the paparazzi. Robert (Harry Lawtey) – a working class boy done good who has struggled to fit in at both Oxford and Pierpoint – finally has financial security, and even some oh-so-unattainable London real estate. Even so, he still falls back on an Oedipal relationship with predatory client Nicole (still played with the perfect amount of pathos by Sarah Parish)

Harper is now persona non grata at Pierpoint, while her former mentor Eric grooms her on/off BFF Yasmin for triumph on the trading floor. So thrilling is the tension between Harper and Eric that it's been described as the most fascinating relationship on TV right now. Having fewer scenes with Ken Leung, who plays Eric, was "so depressing! I was like: 'Where's Ken?' every single day." Her character was similarly bereft, albeit for different reasons. "Speaking as Harper, she definitely feels jealous and resentful of the fact she's being replaced ... but she's also vain enough to think: you of all people can't replace me! But she cares about Yasmin – she doesn't want to be outwardly horrible." So separate is Harper from the goings on at Pierpoint that she doesn't even have any scenes with Kit Harington, who joins as green energy CEO and manchild Henry Muck. (Such is its success that Industry now attracts a revolving door of huge guest stars – the Game of Thrones alumnus being just one – and its status as a sleeper hit has seen it take over HBO's hallowed Sunday night slot from that fantasy drama's spin-off series, House of the Dragon.)

For the 28-year-old, who dropped her last name, Herrold, last year (as Zendaya proved, you don't need a surname to be a star), returning to the chaotic world of Pierpoint and its rivals was "like coming home". Industry was her first big screen role back in 2020, fresh out of a musical theatre degree at Pennsylvania's Carnegie Mellon University, during which she appeared in a touring production of The Book of Mormon. She describes stage as "my first love and my heart's desire", and hopes she can get back to it at some point, though she is also keen to "dip my toes in everything".

Since Industry, her credits have ranged from Black Mirror's smart true-crime pastiche Loch Henry to A24's comedy slasher Bodies Bodies Bodies, plus a Netflix film, Leave the World Behind, alongside Julia Roberts and Mahershala Ali. Among the projects she has in the can is a Social Network-esque biopic of Whitney Wolfe Herd, about "feminism and sexism", in which she plays an amalgam of the Bumble founder's real-life friends. Where she once felt intimidated ("When I see images of season one of Industry, I think: 'Who is that child?!'"), she is now more than au fait with her role, as if she were – like Harper and friends – actually several years into a graduate scheme.

"Harper and I have been together for so long now. In the beginning, they were like, bring as much of yourself to this character as you can, because we are not black American women. No one can play Harper but me – I don't feel any impostor syndrome any more." But I think that also comes with age, it comes with experience. Instead of it being like, I feel unsure about whether or not I can do this, I can say I'm really excited for the challenge"

The world of Industry is notorious for its excess, leading to comparisons with its high-octane HBO siblings Euphoria and Succession. Much has been made of the sexual element of that excess, too; for what it's worth, season three is largely celibate. In any case, viewers will surely be surprised to see just how unexcessive Harper is at the start. It is, Myha'la says, an "emotional rock bottom" for her character, who is "losing brain cells" as a glorified PA to stressy green investor Petra (Sarah Goldberg).

"She's still got the burden of being someone's assistant and not doing the job she knows she's qualified to do, just to hold on to her visa and not get deported. She's just trying to keep her head down, but she's always fighting against the possibility of somebody finding her out. She doesn't want to tell Petra she didn't go to school. That's embarrassing!" It is a treat to see Myha'la pare back some of the character's hotheadedness. Working with Sarah Goldberg – best known for her role in another HBO show, hitman comedy Barry – was also a boon.

"She's the best," My'hala says. "She's incredibly talented. We had great chemistry on screen, and a very nice friendship off screen. I always find that people who have strong comedy chops have untapped drama chops."

In spite of their differing career trajectories, there's still plenty of chemistry between Harper and Yasmin, too, their friendship now firmly in ride-or-die territory. Yasmin's struggles with the press are key to their closeness, and seem to have been more than slightly influenced by real-life headlines – as usual, Down and Kay's script fizzes with specificity, in this case references to the Leveson inquiry.

"Y'alls media are cut-fucking-throat," Myha'la adds with a nervous laugh. "I wouldn't want them to catch me on a bad day. They're ruthless. Hacking people's phones is intense." There are some writing risks that pay off, too – a bottle episode focused on Sagar Radia's motormouth trader Rishi is totally gripping ("I was like, I just know Sagar's gonna eat this up", Myha'la adds). But the main departure here is a series of flashbacks focused on Harper and Yasmin, which explain why even Eric can't drive a wedge between them. While an overwhelming sense of unease coats those scenes, they're also among the most swanky of the season, set on board a yacht in Mallorca.

"Marisa was going to some pretty dark places every day," says Myha'la. "So it was nice to juxtapose the intense shit we were working on with a beautiful atmosphere, good food, friends. I was like: girl you deserve a cocktail after what you've gone through!" Working with Abela, fresh from playing another young woman hounded by the tabloids in the Amy Winehouse biopic Back to Black, was "very symbiotic. She's one of my dearest friends. She's smart and thorough and always brings energy and fire. I love working with her."

Of course, it wouldn't be Industry if Harper went all wallflower on us for ever and, says Myha'la, season three is all about the character "constantly battling between, am I gonna do this very feminist thing and be a normal coworker with a female superior? Or I could go off on my own and do it big? Like what do I do morally – do I serve myself?" Eventually, of course, she "does what she does best and schemes and scams her way into someone else's pocket".

Despite the void that often exists between them on screen, Harper and Eric find themselves in dangerously close proximity, walking into rooms and sensing that the other has just left. "He's plotting her downfall, and with everything she does, there's some thought about how it will affect him", she says. As for Leung, Myha'la found herself on set just as he was shooting his final scenes for the season, among them his half of a tense phone call to none other than Harper. "I was like: 'I'm here! Let me read for you!' I'm really grateful we got to do that scene together." As they say, keep your friends close – and your onscreen enemies closer ...

Industry season three starts on 1 October on BBC One and iPlayer.