Stephen King knows a thing or two about “a good marriage.” He’s been married to Tabitha King for over 40 years, and if it wasn’t for her dipping into the trash can to rescue a young King’s discarded draft of his debut novel, Carrie, we may have never been blessed with the most perceptive and prolific horror writer of any generation’s classic-filled output.

Despite his staggering bibliography, it's rare that Mr. King steps out from beyond his comfort zone to extract the essence of his story and commit it to an entirely different format: the screenplay. In A Good Marriage (in theaters and on VOD today), adapted from his own novella (included in the 2010 collection Full Dark, No Stars), King takes the creepy underpinnings of the very real BTK Killer story and applies it to a thriller about a couple celebrating over 25 years of marriage. The wife, Darcy (Joan Allen), discovers the horrifying secret her husband, Bob (Anthony LaPaglia), has been hiding from her all of those years.

There’s zero stunting in director Peter Askin’s translation of King’s screenplay—no slick camera tricks, dread-drenched cinematography, or jump scares. Focused on the claustrophobic intimacy and normalcy of its characters’ lives, A Good Marriage shines through its lead actors’ understated performances and the question it poses to audiences: what would you do if the person you loved more than anything was a real-life monster?

Stephen King and Joan Allen recently held court with Complex to discuss the darker side of holy matrimony.

There’s a quote in the movie where Anthony LaPaglia’s character, Bob, says, “This isn’t the scene where the husband chases the wife through the house screaming.” That quote illustrates the natural approach this film takes to portray a really “good marriage” gone wrong. Let's talk about the story’s restraint—how nice it was to avoid the hysterics that a lot of psychodramas portray in killer/victim relationships?
Joan Allen: Well, from an acting point of view, this is a man that she has deeply loved for many years. I spoke with Peter [Askin] a lot about that conflict—she gets this unbelievable news about his savagery, but this is the person she's been the most intimate with and trusted and loved. It’s difficult for her to be able to process it, and it takes time. It takes time for things like this to sink into the human brain. It’s like, "This can’t be real," and then after a while it’s like, “It is.” It takes time to take in something of this kind of enormity.

They say write about what you know, and I’ve been married for about 43 years, so marriage is one of these things that I know—but I still wouldn’t say that I entirely know my wife. - Stephen King

Stephen King: There’s a feeling at first when she finds this, that it can’t be true, but the evidence is right there, and, as Joan said, she’s loved Bob for years. We open with an anniversary party—they’ve been married for 25 years, and to discover after all that time that you’ve been sleeping with a stranger, that there’s a stranger inside the body of the man you love or inside the brain of the man you love, that would take a little processing to get used to the idea.

Once you actually internalize that, then you say, “What am I going to do about this?” I know what the right thing to do is, and what I must do, but at the same time I realize that once that is done, it will ruin my life, my children’s lives. Bobby points out that on a financial level it’s going to ruin that part, and so it’s like, how do you handle those things?

Those were all interesting things, and I don’t think that you need to see Bob slitting somebody’s throat. We even play off that in a little bit in the movie where Darcy has the TV on and the batteries are dead in the controller—this awful horror movie is on where people are getting chopped up and everything. In a way, that’s the director and the screenwriter’s way of saying, “This is what we’re not doing in this movie. Everything is going to be between the lines. It’s going to be more Hitchcock than it is Wes Craven.

After Darcy’s revelations, there’s a deepening level of emotion that not many of us can relate to. A lot of people will take a look at this and be like, “Take a knife and go stab him,” or, “Throw him in the trunk of the car!” But I feel a lot of people can’t explain what their gut would make them do in such a situation.
Allen: Yes, I think Darcy has been quite sheltered. She’s been in a very comfortable life, and she has this business; she was probably on the PTA. She was very involved when her kids were in school, and this is so out of her league.

King: Totally.

Allen: It’s like, how do I even begin to deal with it? So she has a tremendous amount of internalizing to do, and she has to make a huge decision that takes a lot of the blush off of the innocence of life. She has to grow up and be exposed to something she would have never been exposed to.

King: Darcy’s had a sweet ride. She’s married to a good guy. He’s got a job and she’s also got a job in the house. She runs his coin business and the two things together make a nice life. So she’s untested in a real way. And when this thing happens, when she discovers what her husband is doing, at first she’s paralyzed by the enormity of it, and then little by little, we see her come to grips.

One of the things that interested me is to see what happens to when people are under pressure. That’s what this movie is really about. Joan carried it, and, to be fair, Anthony LaPaglia’s a great Bob. There’s something going with his portrayal of Bob. You say to yourself, “This is probably what a serial killer is really like.” He’s sort of this ordinary guy with this monster inside.

Joan, this your first time in the world of Stephen King. How was your experience dealing with this character who’s battling doubt, denial, and a range of emotion?
Allen: I had a fantastic time, because of the intimacy of the story and the way it was a small team of people working on it. I had never really worked on anything that I had to play for suspense, and it also kind of has a dark irony to it. It felt more Hitchcock-ian in a lot of ways. I thought a lot about Hitchcock when I was creeping down the stairs to see if Bob was there. It felt like I was in a classic kind of suspense story, and I really enjoyed that.

King: It’s got a lot of twinkles of that Hitchcockian humor, too. One of my favorite lines is when she’s in the garage and he leaves these notes everywhere and one of the notes says, “You can park this if you really try,” and she says, “He goes but he never really leaves.”

Stephen, you’re a big fan of rock ’n roll. It’s been a big part of your work and your life. Is the process of adapting your own short story sort of like the jam version of your novella or is it the stripped-down acoustic version?
King: Stripped-down acoustic version, in this case. It’s not always stripped-down—sometimes it’s electrified. But what I wanted to do to this was give this a real home feel, and I wanted it to be claustrophobic, to actually bring it into their house. I was happy just to be in the house. It was Peter Askin who said, “This is a little bit too claustrophobic for me. Could you please write a scene where Darcy is outside with friends?” So we did that, and there’s a scene where Bob is repairing his car, which is outside, but a lot of it is interiors and that claustrophobic feel. So, yeah, stripped down acoustic.

Marriages have been the center of a lot of my favorite work of yours. Whether it’s Pet Sematary or Lisey’s Story, why do you think marriages, good or bad, can conjure so much horror in all of our hearts and minds?
King: Marriage is referred to in the bible as “mystical union,” and it really is in the sense that two people who don’t know each other get together. I’m always interested in how much you find out about the other person and how much you don’t find out. In the case of Lisey’s Story, that marriage is the basis of strength and love and loyalty and the ability to go on. In “A Good Marriage,” it’s the case of a woman finding out that her husband is not who she thought, which is horrible. They say write about what you know, and I’ve been married for about 43 years, so marriage is one of these things that I know—but I still wouldn’t say that I entirely know my wife.

She’s held you down all these years…
King: She keeps me centered. She also has her secrets, and one of them is in “A Good Marriage.” One night, she was in the bed, and as I came in the room her feet started to move frantically under the coverlet, and I’m like, “Honey, what are you doing?” She says, “Nothing.” So I picked up the coverlet and there were all these little Snickers wrappers there down at the bottom. She’d been sitting there and snacking away at Snickers. But I never left a note that said, “What’s in the fridge today goes out in the bucket tomorrow.”

Personally, what do you both think it takes to make a good marriage?
Allen: I think being compassionate, and really listening. It’s important to really listen to the other person and have them feel like they’re heard, to make sure the relationship feels equal.

King: Trust, a sense of humor, and don’t let the sun go down on an argument without trying to make it up. That’s all I know. I’ve been married a long time—it seems to be working.