In director Steven Soderbergh’s just-released thriller Unsane, British actress Claire Foy (The Queen) plays a woman named Sawyer Valentini held against her will at a treatment center whose employees include the stalker (Josh Leonard) who has been hounding her — or so she claims. The movie was shot in secret, on an iPhone, and costars Joshua Leonard, Amy Irving, Juno Temple, and Jay Pharaoh from Saturday Night Live.

“I got sent the script, and Steven was in London, and they said, ‘Do you want to meet him?'” says Foy. “I was like, ‘Yeah, okay, I’d love to meet Steven Soderbergh. And then he asked me to do it. So, it was a bit weird. I never at any point thought it would turn into anything. It was such an honor to meet him and then I got to work with him as well.”

ENTERTAINMENT WEEKLY: Did this role require much research?
Well, obviously, the American medical system is very different to the one that we have in England. So, a lot of the time, I was reading the script and going, “Oh, come on, why would anyone ever do that?” And then I researched it and went, “Oh, dear God! No! No!” I looked as much as humanly possible into how hospitals like that are run, and what the procedure is, and things like that, and I obviously researched people who are victims of stalking, and harassment, and things like that. But it was a limited time. We shot for 10 days. There was no rehearsal. It was very much a thinking-on-the-job kind of job, and that’s really why I loved it, because it was very much about just throwing myself in, and not second-guessing myself, and just trusting.

It must have been surprising and horrifying how much more relevant the themes of the film have become over the past few months. I mean, your character is being gaslit, restrained. This could hardly seem more of the moment.
The concern about saying it’s “of the moment” means it’s not something that people have been struggling with or thinking about for a really long time. If you try and make in the zeitgeist, you negate the fact that this has been going on since the dawn of time. It’s not something that is a flash-in-the-pan situation. It’s part of pop culture, it’s part of the reality of the society that we live in, unfortunately.

I apologize. As I was asking that question, I could hear every female acquaintance I have telling me in my head that I’m an idiot.
[Laughs] Yeah, yeah. [Laughs] I can tell you, too. You’re an idiot! There you go.

The film was shot on an iPhone. How much of a difference did that make to you?
Well, a camera is a camera. But the thing I loved about it was that Stephen was in the room, he was operating [it], so it really felt like he was there, watching everything, being part of it, which felt really amazing. I’ve never had that before. It meant that we could get a lot done. We shot it in 10 days, and it meant Steven had huge amounts of freedom in where he could put the camera, what he could do with the camera, what he could try and then get rid of. He was just experimenting all the time. We shot it entirely chronologically. It just moved. It just moved a lot. And it had an energy, and a rhythm, and a momentum to it that felt fresh, and unrehearsed, and full of life.

No one knew this film even existed until quite recently. Did Steven ask you to keep it quiet?
He didn’t ask me to keep it quiet. But he was like, I want to make a film, I want to go back to basics, I want to learn. And that’s what I felt like. He just doesn’t agree with the system, he doesn’t agree with the way the system works. He doesn’t agree that we should have to announce the film. I just admire that quality so much. Our industry could do with more people who feel that they can work outside the system and not be told what to do all the time.

Could you talk about your costars? You’ve got a lot of people from very different backgrounds: Amy Irving, Jay Pharaoh, Josh Leonard.
Amazing. Joshua Leonard, we got in the car I think on the first day, and I was like, “You have to play my stalker!” [Laughs] But we just got on like a house on fire. I just really really got on with him, which really helped. If he had been method and odd, I think that would have freaked me out. He even sent me these jokey messages saying, “I know where you are!” And Juno Temple, I just think is — I want to be Juno Temple.

I think everybody wants to be Juno Temple.
Everybody surely to god wants to be Juno Temple. She is amazing. It’s like she’s in her own ’70s film all the time. I just love spending time with her. I find her so exciting and alive. And Jay was amazing, so funny and so clever. And I loved Amy. It was a really, really lovely job. Everybody, we were all barely there, because Steven shoots quickly, but it just had a feeling of equality, and joy, and humor about it. I loved it.

You have presumably seen the finished film. What was that like?
I loved it. Anything in the hands of Steven Soderbergh turns into something completely unique. [He] wasn’t saying this is the best film ever made. The point was, we were making something, and it was also an experiment, and an improvisation, in a way. It’s so full of clichés, but also done in a way that means it’s unique, you know what I mean? It’s all tongue-in-cheek. And you’re not an idiot.

Unsane is now in cinemas. Watch the trailer for the film above.