Lena Headey. Photo: Alberto E. Rodriguez/Getty

In the near-future America of The Purge, one night a year is reserved for violent crime: For twelve hours, the state sanctions, and even encourages, otherwise illegal behavior, including murder, with no criminal consequences. The idea is that the rest of the year there would be less crime, though one of the outcomes is that the Purge results in more crime against the lower classes, who can’t afford to protect themselves. One family that can protect itself — theoretically — is headed by Lena Headey and Ethan Hawke, who has gotten rich from selling security systems to his resentful high-class neighbors. Their plan? Lock themselves indoors and wait it out while Purge participants rape, maim, and murder with glee. Of course, this being a movie, things never go according to plan — not when you’ve got an underage daughter with an overage boyfriend, a son who empathizes with the downtrodden, and neighbors who exclude you from their Purge plans. Headey, who also plays the formidable Queen Regent on Game of Thrones and knows a thing or two about bloodlust, chatted with Vulture about purging violent emotions, a mother’s love, and why her son thinks she’s out fighting ninjas.

As a concept, do you think a “purge” could actually work?

I don’t think it should ever happen, no. It’s a fucking horrendous idea. But the concept is a many-levels concept. And as a horror-action idea, it’s kind of a great idea that’s based somewhat in reality. Does our culture have a need for violence? I don’t know. I guess it’s a personal thing. Some people fucking hate horror films, right? But I love them. I find Chainsaw to be a very relaxing film. [Laughs] For me, horror movies are a real escape. I don’t feel like I’m getting anything out, but my brain shuts down, [sigh of relief] and I can fall into this dark, you know, fantasy for a minute. I don’t get anything out of it. I just go, “Oh! That was nice.”

Do you feel like video games are a good release to purge or vent when you’re angry? You can let out any desire to hurt someone without actually hurting anyone.

Video games might be relaxing, too, but I don’t play them, so I don’t know. You can do that, or go to the gym. Punch a punching bag. I think I cry when I’m angry. I let it go that way. I’ll have a fucking rage, drink a little bit of wine, have a cigarette, get it out. Or I’ll have a good sob. Or I’ll meet up with friends and have a laugh. Watch a film to cry, like a cleanse. I never put one on thinking I’ll cry. You know the last thing I cried at, which I thought was a really beautiful movie, was The Perks of Being a Wallflower. I watched it on the plane, and when I got off the plane, it was like I had eaten a balloon or something. I just found it incredibly well done and moving and honest. That was the last thing I cried at involuntarily.

I can’t help but cry whenever there’s a scene in a movie like Terms of Endearment, when a mother is dying and the kid is being bratty and he just doesn’t get how much she loves him.

Ah, the classics! Yeah, I don’t think I can watch that now that I have a kid. It’s amazing the things that you cry at. I cry when I smell my son’s hair in the morning. We have a moment of peace and I’ll be like, “Ahhhh! How can you love this much?”

You’ve played a number of fierce mothers beyond The Purge — Sarah Connor in Terminator: The Sarah Connor Chronicles also springs to mind — before and after becoming a mother yourself. Did your portrayals change once you had a child of your own?

Definitely! That scene in The Purge where my kids, Mary’s kids, are in danger was really crazy for me, because I suddenly … I have my methods as an actor, so I went to the place of “If somebody came near my children, with bad intent?” It’s a feeling without a lid, of what you would do, physically, verbally, to protect the one thing that is your greatest love.

Is that what Cersei is doing? Because sometimes it seems like she’s afraid of her own child. It must be hard to love a monster.

[Laughs] My God! That’s a love that isn’t love. Sometimes it’s a bizarre, fairly cold, and horrifying thing to be a parent. But it helps me to do those scenes because Jack [Gleeson, who plays Joffrey] is such a joy, and I have a genuine love for Jack. I kind of look at him like, Wow, you’re such a cool kid. I believe once we just started rapping together on set, making up words on the spot to make up a song. He can be really funny. He’s absolutely adorable.

You were pregnant when you started shooting Game of Thrones, season one, and I didn’t realize it at the time, partly because during your sex scene with Jaime, you don’t disrobe since he takes you from behind.

And also, that scene, it wasn’t me. [Chuckles]

Ah, a body double.

I’ve said from day one that I’ve got no problem with nudity. I’ve done it throughout my career. But for this character, it’s been better for her regality and her feistiness to not bare her flesh until she has to. When it’s out of her control. And if that ever happens, it won’t be Cersei being seductive or sexy. She’ll be stripped. That kind of a scene will have more power if it’s not an everyday occurrence. I can’t wait for that. But after that scene, we just hid the pregnancy. But even after that, I’m not a naturally pregnant person, so I was having all these hideous post-pregnancy hormonal moments, mentally, and that’s a completely other thing — I was not happy. But that helped for playing Cersei. Hold on, my son’s asleep, just one second …

[Shuts a door and whispers] It’s his mid-afternoon nap, because he’s just back from preschool. Our day begins at six, and I told him this morning, “Mommy’s really tired this morning. The dog kept her up all night.” And he said, “But I don’t like it when you’re tired.” What he really doesn’t like is whenever he sees a vulnerability.

Does he like it when he sees you playing these strong women on set? Does he go to the set?

[Still whispering] He doesn’t fully grasp it all yet, obviously, but I took him to the set of 300: Rise of an Empire, and we were fighting with swords, and of course he loved it. I started to film a scene, and he yelled out, “Mommy, beat ninjas!” And I said to him, “I love that you have my back.” “Ninjas! Mommy, beat the ninjas!”

He sounds adorable.

[Still whispering] It’s heaven right now. Although … I said to my girlfriend, because he’s always going, “Mommy, why this? Mommy, why that?” all day long, that I told him, “Okay, next time, think. Is it something Mommy needs to know?” But we’ve been playing a lot of ninjas together, the two of us — lots of ninjas and pirates games. Very loud ninjas. Hopefully the neighbors haven’t noticed! I love our neighbors. We’ve got some very cool Brits near us, and I would never want to kill them for anything.