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In previous interviews about her role on True Detective, Michelle Monaghan has described Maggie, the long-frustrated wife of Woody Harrelson’s Marty, as “devastating” and “cunning,” terms that didn’t really seem to jibe with her character’s persona until Sunday’s episode, “Haunted Houses.” Turns out that Monaghan had been teasing the blunt but highly effective means Maggie used to cut ties with her philandering husband. [Warning: Spoilers ahead for anyone who hasn’t watched through episode six of True Detective.]

Even though Maggie targeted Rust like a heat-seeking missile and seemed intent on doing so to hurt Marty, Monaghan says having sex with her husband’s partner wasn’t entirely about getting even. Vulture spoke with the actress about filming the game-changing moment with Matthew McConaughey and why she doesn’t agree with critics who’ve said that the show’s female characters could be better served.

So this is where “cunning” came in.

Yes, that’s correct. I think her decision to sleep with Rust was the ultimate betrayal and revenge for Maggie after what Marty’s done to her. It was the only way that she could save herself and save her family. She had to devastate him in such a way that he would leave them alone forever.

And because this is a limited series, did you know from the outset that this was where Maggie would be heading?

Yeah, that was all in the cards when I signed on. It’s what ultimately made me sign on, really. It was such a great arc and a very unexpected one.

I can’t imagine things can get any darker for her.

I would say her story continues, but this is sort of the pinnacle of it.

How tricky was it to shoot that scene with Cohle? It all happens so fast.

Originally, it was split into two scenes. As we rehearsed it, there was the scene where we do the deed and then he’d go into the bathroom, come back out, and then I tell him what I’d done. But as we kept rehearsing that post-coital moment, it felt really, really heavy and still, and I thought that what would really happen there is that it would continue on. I would just get it all out there. It wasn’t a moment where I would hang out and wait for him to go the bathroom. Maggie would reveal what she’d done right away. She wouldn’t play any more games, and she wouldn’t want to. That would be the extent of it.

Did you have to talk about it, or did you and Matthew McConaughey just instinctually keep going?

We just went for it. I mean, we filmed it over the course of a few hours, different parts of it. But what you saw, it was a “wham, bam, thank you ma’am” deal. It didn’t take us long to figure it out. We just looked at each other and said, “Let’s just do this.” So we did. The first time, I turned around and kept going and it felt really raw and the energy was explosive. So we stuck with playing it all out right there in that span of time.

She’d connected with Rust from the get-go, and clearly felt sorry for having to use him like that. But why did Maggie get on so well with Rust, who has trouble connecting with people?

Well, he’s open with her. In comparison to the relationship that she has or doesn’t have with Marty, Rust, to her, is very much an open book. Marty is closed off. He can’t connect with Maggie and Maggie’s a very inquisitive woman. She’s not afraid to try to engage Rust, and he always seems to be very forthright with his answers — even though she may find them a little bit ridiculous [laughs]. They’re able to have a conversation like adults, whereas she can never have an honest conversation with Marty because he shuts her down each and every time. I think that’s why she develops a rapport with Rust, and why it’s so devastating for her to have used him in the way that she did. She realizes that’ll be the end of her relationship with him as well.

How did she know he’d succumb if she were to try to seduce him?

I think that she understands that he’s vulnerable, that he’s also a bit of a tortured soul. And I think when she walks into the apartment she can see that he’s been drinking and it dawns on her that it’s going to be a little bit easier than what she thought it was going to be.

When we met Maggie in the first episode, she was already very bitter about her marriage. What insight did series creator Nic Pizzolatto give to you about how her relationship with Marty had gotten to be that way?

They’ve been together at this point for about ten years. She’s seen a man that’s just consumed by his work and doesn’t have any time for the family. Drinking is clearly an issue in his life. Infidelity is an issue. She just recognizes that he is no longer the man that she’d always known, and that’s a very frustrating place. To create a family with someone and then watch that person not evolve with you or grow up and change and put their best foot forward with you. She’s at that point when the story opens. And what pains her the most is he’s not just disconnected from her but also his own daughters.

The drama’s central relationship is between Rust and Marty, but one of the critiques the show has gotten is that the female characters are underwritten. What’s your take?

I never saw that in my role at all, I guess because I saw the entire arc of Maggie and I understood this character. I thought she was fully fleshed out, I thought she had a very interesting and complicated relationship with two men and it unraveled in a very devastating and intimate way, and a really honest way. I felt very connected to it. I never really questioned that going into it.

You and Woody Harrelson have been friends for years. [The two met while making the film North Country in 2005]. Does that make it easier or is it strange to have to play characters who are so hostile to each other?

Woody and I have never had an argument, so it was weird! There were some pretty explosive moments, and we would finish the take and he would quite honestly say, “Oh my God, I did not know you had that in you. I did not know this about you.” But it was fun getting to play that with a friend. What I love about Woody in real life is that he has this incredible boyish charm that is so endearing. He sort of utilizes that in the role of Marty a bit, and it’s something that always gets Maggie. He plays the vulnerable little kid who’s struggling and I think she falls for that every time, even when she knows better.

There are a lot of theories cropping up online about the identity of the Yellow King/killer. Did you have any of your own as you were getting scripts?

Completely. I mean, it was such a page-turner. You can’t put it down. It’s like reading the best book. So of course I was coming up with my own theories, I’d say from episode three on.

Maggie’s dad was on the list we compiled.

Oh, my gosh. People are really into the show and it’s a great thing. I have people coming up to me, telling me their own theories, and telling me to give Marty another chance.

What? Who are those people?

I know! “He’s just having a tough time. Give him a break!” I find it so fascinating.