Caroline Kepnes did not think she was writing a book about a serial killer until after she finished You.

“I never used that phrase the whole time that I was writing,” she says firmly over coffee on a crisp Friday afternoon. “I remember finishing and my friend told me, ‘I can’t believe you wrote about a serial killer.’ I was like, ‘No, I didn’t. He just killed a few different people.’ She asked, ‘Do you hear yourself?’ And I realized, Oh, God. That’s what people are going to say he is.”

The “he” is Joe Goldberg, a 20-something bookstore manager from Brooklyn who begins obsessing over a grad student who walks into his shop one day to buy a novel. Her name is Guinevere, but she goes by Beck, and Joe interprets light flirtation as irrefutable truth that she came to find him—that the book was an excuse; that their encounter was love at first sight, rather than one of the millions of random encounters people have throughout their lifetimes. He begins to follow her, thinking that he is her protector, all the while talking to her in an inner monologue. And yes, along the way, he kills people: a trust-fund bro Beck was sleeping with; a best friend he believes was secretly in love with her. Eventually, he kills her too.

“He feels like he has really bad luck,” Kepnes offers of her villain, who operates under the rock-solid belief that everything he does—the stalking, the gaslighting, the murdering—is for some greater good. For true love, actually. He is quick to judge and even quicker to condemn, and pities the people in Beck’s life whose standards for living he doesn’t agree with. He’s “holier than thou,” Kepnes points out, and operates from a moral code that allows him to believe he’s doing people favors by killing them.

You was first published in 2014, as a stomach-churning second-person narrative designed to make the reader feel like Beck through forced perspective in which Joe attempts to convince you that everything he does is all for you; a second novel, Hidden Bodies, was published in 2016. You came to Lifetime last September, as a series starring Penn Badgley and Elizabeth Lail as a millennial cat and mouse. A few viewers caught on, but perhaps some people’s preconceived notions about the network kept the series from achieving mainstream appeal. It was only when the show hit Netflix, shortly after Christmas, that it hit a critical mass. People became obsessed with Joe, and obsessed with his obsession with Beck.

Kepnes now calls that second life a “bizarre” experience to have been a part of. “There’s so much out there, so there’s no way to know,” she points out about the seemingly endless options that people can stream, and binge, and talk about with their friends online. “And suddenly it was like, this book is the thing that everyone’s talking about. I still can’t wrap my head around it.” Old friends reached out to her, saying they had watched the show. Fans congregated on forums, discussing the details that had read as normal courtship upon first watch but contained sinister undertones they’d never noticed before. And Kepnes watched in real time as people used social media—something Joe obviously disdains in both the book and the show—to dissect every melodramatic moment and each thing they hated about Joe, while also recognizing him in other dangerous relationship tropes, and, in some cases, loving him.

When Badgley, who plays Joe, discovered fans camped out in his mentions because they were attracted to his character, he first tried to correct them, in a series of exchanges that went viral. Kepnes, however, understands the pull. “He’s also very sweet in a few scenes,” she points out, alluding to the times Joe acts like a kind, normal boyfriend, even as those moments become material for Joe to later gaslight Beck.

“That was my whole drive for doing this,” Kepnes adds. “How did these men get through the day? How does it work in their head? I feel like our culture overall is very hard on women who love the wrong men, but strangely not as hard on the men for being wrong. I think it’s because the assumption is that he’s a monster and you should have gotten away.”

Perhaps we as a society are more willing to talk about monsters now that some of them are beginning to face real consequences for their crimes. And maybe we are simply growing so comfortable with social media that more and more people are open to expressing their fears, and how they can be inexplicably drawn to them. But You’s television adaptation also hit a critical mass around the time that Netflix released a four-part documentary about Ted Bundy’s confession tapes, and a buzzy movie starring Zac Efron as Bundy premiered at Sundance. Both films were directed by the same man, released around the 30-year anniversary of Bundy’s execution, and seemed more interested in getting into the killer’s head than offering justice for the dozens of victims he killed.

Serial killers seem to always be in the public consciousness, but Kepnes is adamant that when she began writing You Bundy was the furthest thing from her mind. “Joe is fiction,” she says, drawing a line. “I feel like that’s where—especially living with social media and so many images, it starts to feel like nothing is real. But Ted Bundy is a real person who killed real people—girls, whose families lost them.” Basing a character on such a person, one who has gained a questionable amount of infamy over the years, she says, would be “perverse.”

She says she loves American Psycho, by Bret Easton Ellis, a book whose pages-long tangents on wardrobes and Whitney Houston rattle around in the reader’s brain in an unsettling way; similar passages in You echo that stream of consciousness. The reader is in Joe’s brain, privy to his every thought. And because the book is written in second person, which Kepnes points out is an “absolute command” at times, readers are constantly told that they are Beck, and that Joe is following them. Though Kepnes says she did worry a bit that going so far inside Joe’s head would allow the narrative to justify and absolve his trespasses, she maintains that the justification is the point.

Like the Bundy tapes, she says, “this is an artifact. And I wanted that to be on every page, to show that this is a fucked mind, and that those people are out there and you won’t necessarily know it. You don’t know the way someone’s thinking about you.” As Joe himself says when he meets Beck’s therapist, “he could be a serial killer or the nicest guy in the world, but there is no middle ground for this dude.”

True-crime stories like You, and the canon of shows, movies, and books like them, also assuage an inverse kind of fear, for women in particular: that we have not been imagining things, and that things do go bump in the night. But rather than reinforcing the idea of stranger danger, as the writer Chelsea Summers pointed out on Medium, stories like this one remind us that monsters aren’t just under our bed, but sleeping right beside us. Statistically, this is true: Over half of all female murder victims are killed by their partners, many of whom exhibit signs of emotional or physical abuse before the victim’s death. Bundy was an outlier. More common are the Joes, the people we willingly date until we realize their danger, or until it’s too late.

But that is a risk we take every time we swipe on a dating app, or show up for a blind date, or chat up a cute stranger at a bar and give little details about ourselves. “To get close to someone,” Kepnes warns, “you could be creating the possibility for your own death.”

Kepnes tried to write the book from Beck’s perspective at first, she says, but she was too inside her own head for it to work. She began working on You shortly after her father died, and gifted a number of details from her own life to her doomed heroine: She lived on Bank Street and West Fourth, in a rent-controlled apartment, when she lived in New York; she is from Cape Cod, but made Beck a native of Nantucket, another seasonal destination; they both went to Brown. She had better friends than Beck did, she says with a laugh, but points out that we only ever meet Beck’s friends—Chana, Lynn, and Peach Salinger—through Joe’s eyes. And because Joe is primed to hate them, we only ever see their worst qualities.

“For all we know, Peach might not be as bad,” she posits. “He’s demonizing anyone who gets in his way.” She points to the way rom-coms always make the surprise fiancé absent-minded, or careless, or a monster. “We know Matthew McConaughey’s not really going to marry that woman,” she says, “but in real life, his character probably would have been engaged to someone who had a heart and a soul on some level. It would have been a little more painful. But wouldn’t it be nice if she was awful?”

To play up that awfulness, Kepnes gave the friends somewhat ridiculous names: Peach, Beck, and Love Quinn, Joe’s love interest in Hidden Bodies. More ridiculous yet is Love’s twin, Forty. “I loved the idea that love is nothing in tennis, and 40 is almost worse than nothing because you almost won but you didn’t win yet,” Kepnes says.

“But with Joe, it was this thing that, like, what would irritate him the most?” she continues. “His name is so common, and it’s that hypocrisy where, on the one hand, he feels he’s so special, and that special people have simple names. On the other hand, someone thought about that person and cared about her enough to give her a name like that, and that gets under his skin.”

It’s getting under Joe’s skin and exposing the mind behind his abusive behavior that drives Kepnes, more than the idea of creating a gore fest. As in American Psycho, relatively little real estate in You is allotted to the actual murders.

“Putting all the murder aside, so much of it, to me, is about how we process emotions when we’re living in a world in which it is always possible to make a public statements,” she says. “I’ve never been more interested in a narrative that’s about the difference between what we’re thinking and what we’re saying. I think that we’re under this pressure to present ourselves the right way on these platforms, and it does get to be this idea that there is such a thing as a perfect person.”

There isn’t, of course, and yet Joe has built Beck up to be the perfect woman for him in his head, in part because he has instant digital access to her thoughts and can therefore mold himself into what he believes to be the perfect man for her. Love Quinn proves more of a challenge; she’s not on social media, and Joe cannot read her so easily. Moreover, he’s in Los Angeles, in a world filled with actors and acting hopefuls; Kepnes calls it a “naive and sweet” city.

“That’s why I love L.A.” she adds. “It’s the idea that everyone’s there with a dream, and they think, Maybe it will be me. There’s something very vulnerable about that. People think of it as a cynical town, but there’s something very pure about wanting to be there. But that’s what makes it all the more disturbing, the way people are so disposable.” After all, L.A. is where killers treated girls who had run away from home to chase Hollywood ambitions like prey, where the unsolved Black Dahlia murder was committed, where Manson’s followers killed Sharon Tate.

For the third book in the You series, Joe will head to the Pacific Northwest; Kepnes says he has decided the problem isn’t him, but city life in general. “He wants small-town life,” she explains. “He’s been reading romance novels and really sweet books in prison, and he’s really inspired and believes that there is a sweet world to be found.” But there isn’t, in part because no matter where you go there you are. Joe is his only constant. He is trapped in his own head, which will always see him as the wronged party and the victim.

Beck, however, learned at an early age that small towns aren’t the answer to your problems. “When you grow up in a tourist economy, and in a seasonal tourist economy especially, people come in to get what they want and then they leave,” Kepnes says, pointing to Beck’s upbringing in Nantucket, where she learned that summer always ends. “I feel like she really internalized that idea that her value is for people who are going to leave her, and that it’s not personal. It’s just the way to the way of the world. Being left is a matter of fact.”

That is part of the reason, Kepnes says, she “always knew Joe had to kill Beck.” It’s an ending she fought at first but eventually added. “Because he doesn’t love her. He wants to control her. And in that way he doesn’t understand what love is like. So he’s always going to keep killing, because that control is an unattainable goal.”