It took a long time for the actor to find her groove – then the smash TV spy thriller changed everything. She talks about getting advice from A-listers, speaking her mind, and why she’s switching to theatre

Sandra Oh bursts into a back room at the National Theatre in London with wayward post-rehearsal energy. The 54-year-old, long one of the most stylish actors in Hollywood, is in brown linen, a herringbone jacket and hat and sunglasses, which she removes before collapsing into a chair and throwing her head forward, arms outstretched, hair splayed across the table. “It’s just the fucking process of it,” she groans. “We just finished our first stagger-through, which if anyone is an actor – it’s early days, so the fact we made it through was great. It’s brutal. We started in the Lyttelton, and it’s interesting to be in that space and to hear verse. You can really hear it. It’s not just about volume or speed. It’s not even solely about intention. You learn so much just being in that space, but the big thing is – sorry.” She catches herself. “I’m just marching on.” And she bellows with laughter.

Oh has been in London for just over a month rehearsing her role as Alice in a modern reimagining of Molière’s Le Misanthrope. It’s a happy return; eight years ago, she was in the capital to film the first of four series of the hit show Killing Eve, which became a phenomenon and changed her life as an actor for ever. Oh played Eve Polastri, the shambolic but brilliant British intelligence agent, who, along with Jodi Comer’s Villanelle, made for one of the best spy capers of recent years. Now, she is playing a novelist – gender-flipped from the 17th-century original, in an adaptation by Martin Crimp – who is fed up with the flattery and dishonesty of the people around her. It’s a deliberate pivot to theatre; last summer, she appeared as Olivia in a starry production of Twelfth Night at the Delacorte Theater in Central Park, New York. In the autumn, she made her debut at New York’s Metropolitan Opera in a production of Donizetti’s comic opera La Fille du Régiment. Unlike the sometimes fraught me-me-meism of screen work, says Oh, working in theatre in general and at the National in particular “is a collaborative thing” – not least, she adds drily, because no one does it for the money. “Everyone has to bring their best and most open selves. And everyone else loves watching everyone succeed.”

Furious fans, bloated storylines and television seemingly made only to sell merch … it’s time to stop dragging series out. Most of them deserve no more than one outing

Though it aired almost two months ago, fans are still angry about the Stranger Things finale.

So disappointing was the wrap to the five-season sci-fi that its cast are still having to deny that there is an upcoming secret final episode. I was not remotely disappointed, however. I thought the show ended perfectly: when I stopped watching it after season one, episode eight.