Ruth Wilson likes to go weird. This much is evident of the award-winning Luther and The Affair star in her latest series, The Woman in the Wall, in which her character, Lorna, may or may not have killed a woman before hiding her inside of her home’s walls. The twisty limited series, created by Joe Murtagh, plays with genre conventions like horror and mystery, with Wilson dialed into its center as a sometimes quirky, sometimes devastating character piece. Beneath the surface of Lorna’s sleepwalking and idiosyncratic speech patterns, the actor was engaged in a canny game of whodunit, playing with perceptions of Lorna’s madness by way of teasing whether or not she really committed the crime—or even knows if she did it.

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It’s a crafty, nimble, ultimately powerful performance that feels like another Wilson signature—and that grounds a story of notable social impact, particularly in the UK and Ireland where the show aired last year. The Woman in the Wall examines the traumatic legacy of the Irish Magdalene laundries, essentially a trafficking ring run by Catholic nuns who took in unmarried, pregnant, isolated women and separated them from their children. (The last of these laundries closed in 1996.) Lorna, we learn, is one such woman who’s been shaped by that horror ever since she was sent to a laundry at 15 years old. As the investigation into the murder of the dead woman in Lorna’s home—as well as the subsequent death of Father Percy, who helped run these laundries—heats up, Lorna realizes she and the detective on the case (played by Daryl McCormack) are connected by their history with the laundries and the pain they continue to inflict in the present day.

The finale, which aired Friday on Paramount+ with Showtime (the whole series is now streaming), reveals that Lorna did not in fact initially kill the woman, but hid her body after fearing she’d killed her in a sleepwalking daze, which ultimately led to her death. (In reality, the woman had suffered an episode due to her catalepsy.) Lorna is presented with a choice: claim she’s mad and potentially avoid charges, or admit in lucidity to what she did. She chooses the latter option—staking a claim for her agency, for one thing, but also paying off Wilson’s intricate balancing act. Then, in the series’ closing moments, Lorna learns the fate of the daughter from whom she was forcibly separated as a teenager: She’s alive, raised very far away, but with the potential for reconciliation.

In her first interview about the ending of the series, Wilson digs deep into just how tough it was to get Lorna and The Woman in the Wall right.

Vanity Fair: You only got the pilot to this show when you signed on. So you weren’t aware of your character’s arc before committing?

Ruth Wilson: Not really. Joe talked me through his plan, but as he was writing and as we were filming, some things changed. What happens to Lorna at the end, that was always in their plan. I didn't always agree with the end—I wanted her to have full justice and I wanted her to be free and to be reunited with her daughter. But in some ways I felt the end was representative of the real experience. It's not as easy as: Everything's tied up in a neat bow and everything works out for the best. There are still questions unanswered by the end. What I liked about it in the end is that she is given a choice of: Do you want to claim you are mad and say you are mad and try to get away with this, or do you want to go down for something that you did? And in her mind she's like, “If I say I'm not mad, they've claimed I'm mad my whole life.” She decided to own her voice despite the consequences.

It frames her in an interesting way too, this question of madness. This is both a genre piece and a character drama. To what extent did you want to signal this potential slipping grip of reality?

Initially she is as lost as we are, as an audience. She's lost in her trauma and in some way isn't quite in control of how that's manifesting. But there's an anger in her, a sort of rebellious nature and a kind of fuck-you attitude that creeps out as the show goes on. She starts to accept who she is, accept that madness: “Well, I've got nothing to lose. There's a woman in my wall and I've done the worst thing I can possibly do, so fuck it.” She meets herself somewhere in the show and that gives her strength and a sense of purpose and a sense of direction. Through that, she sort of becomes more clear and less mad in some ways. That was really fun to play, challenging people and not caring about the consequences of it.

When you found out essentially what she did and what the end result of that mystery was, how did that impact the way that you played her? You as an actor know the truth, even as the audience is guessing—and the character is guessing as well.

It was quite hard. There were two things happening all the time, which I found a constant challenge. That was the journey of this woman in the wall, which: Was it real? Was it not? It's always slightly muddied as to, is that part of her reality or not. And then there was this other side of finding her child, which felt very real to her. So I'm holding those two things in my head at the same time, quite difficult to do as an actor because they're not working in the same story threads. So if the scene required me to be thinking purely about the woman, I’d think about the woman. If the scene required me to be thinking purely about the child, I’d think about the child. To marry the two was difficult. I just had to be more present in the moment—serving that character moment to moment more than I’ve ever done before in a show. I felt like it needed quite sharp delineation depending on the scene.

You have a lot of fun with this character. Given the weight of the story, there was something really gratifying about that choice for me, to have her be that kind of personality. Can you talk a little bit about bringing that relatively comic side out, and what that meant to you?

It was essential to me. I found Lorna funny. I found what she did really funny and really surprising. At the end of that first episode, I was like, “Oh my God, she's just knocked down a wall and put this woman inside it.” I just did not see that coming. I thought, She's a quirky, eccentric, and provocative character that you can't explain and you can't really trace where it comes from. There's a line in the first or second episode where Michael says to her, “You were the funny one.” Traces of who she was when she was a kid. Then I thought, Okay, well she's an outsider. I thought about Patricia Highsmith. She's batshit, right? She's completely batshit. She was seen as an outsider and she could kind of get away with it because it added an air of mystery to her. She probably did things to provoke. That was interesting. I don't know if Lorna is doing things necessarily to provoke—she is later on—but if you are an outsider, you gain a bit of power with that because people think you are weird anyway. So I'm going to act more weird! I had loads of fun.

I was thinking of Luther a little bit where it's almost the inverse for you—with Alice, you’re bringing wit to a psychopath. But it’s an edge I notice a lot in your work.

Yes. It's a deliciousness. With Alice, it's all about a place for me to go somewhere where I can psychologically justify it. I remember reading a book about the idea that all emotions, they're just energy—when I was 28, the first time I read it, I was like, “Wow, that's really interesting.” [Laughs] If someone knows it's just energy, they can remove themselves from the emotion. Alice doesn't feel like anyone else. She knows it's just chemical and just energy. So every human's a play thing because they're idiots, they fall for the trap of emotions. She's just a cat with endless play things around her. You want to find the humor. I think it's sort of gleeful, these characters. They're on the page to be a bit gleeful and to have a relationship with the audience. They're not purely just baddies or goodies. There's something in finding the other side.

You’re an executive producer on this. Given what you were saying about having mixed feelings at the ending, how did you find that creative collaboration?

So they asked me to come on as an EP and as an actor. From that stage on, we got into the room and were working on the writing of it. I thought it was really important to have a female in the room. There were lots of male producers and Joe, but because it's such a female-led story, I thought it was vital to have a female presence. As long as we landed that story about the women, as long as those stories got out there and we affected people with those stories—that was really important to get right. So that was part of the process of being in the room with the writers and then in the process of shooting as well. And yeah, we had different ideas about what an end might be. I questioned the end, but then I thought, actually I quite like that it's bittersweet. There are still people who have gotten away with what they did. There was part of us feeling we needed to represent that in the show somehow.

This show aired in the fall in the UK and obviously you shot it well before that, so it's been a lot of talking about it—a lot of important stuff to talk about. You're also being a kind of spokesperson for this subject and what the show brings to light. How do you look back on the experience of both making the show and really getting the word out?

It's been a mad process actually. In the process of development and the process of filming it, it was a tussle because we were dealing with something quite unique—you're going in blind and you don't quite know if you're landing it or not, or if the tone works, the comedy alongside this darkness alongside the horror tropes. You don't really know. That can be really exhausting because it means rewrites, it means everyone's working at 200% to try and work out what this thing is. The same within the edit.You're still shaping it in the edit, you're still going, “What is this? I don't know.”

I remember not really knowing what it is. You never do until you put it out into the world. And even then you're still not sure. But it went out and I was really thrilled at the reaction we got in the UK. So it came out, what, six months ago here? I couldn't have been happier with the way it went down. It did exactly what we wanted: Every newspaper did a big deep dive on the Laundries and the mother and baby homes, and people that hadn't heard about them were hearing about them for the first time. They were seeing it dramatized in a really emotional and wild way. What it entrenched for me, I suppose, about the work that I do is that I knew it had something to say and it was worth doing for that reason, despite all the challenges of it. And to have that validated and people around the world seeing it for that reason—I am really proud of it. I probably won't watch it for a while, but I'm proud of the risks we took.

This interview has been edited and condensed.