The franchise's newest chapter, Pretty Little Liars: Original Sin, arrives on HBO Max July 28.

What would become an expansive world filled with teenagers, secrets, and murderers started as a simple assignment: What's a teenage Desperate Housewives?

In the early 2000s, Desperate Housewives was a massive success, and Alloy Entertainment, coming off the success of the Gossip Girl book series, wanted its next big hit. Leslie Morgenstein, Alloy president and CEO, remembers being part of the team that was tasked with creating a teenage version of Wisteria Lane.

"We broke it down a little bit and fundamentally, Desperate Housewives was just a primetime soap with a murder mystery. And it had, at the beginning, an anonymous narrator," Morgenstein tells EW. "So we batted ideas back and forth and we landed on the starting point for Pretty Little Liars, which was four best friends start getting tormented from their fifth best friend who went missing years earlier. And that character became 'A,' in the books."

Alloy was already in business with author Sara Shepard at the time, who quickly took to the idea of creating a story with more edge to it. Drawing from her own life, she then started to build out what would become Rosewood. "I grew up outside Philadelphia and everybody seemed perfect. But behind closed doors, these families that I thought were totally amazing and had it all together were really struggling with things," Shepard says. "The main characters were based on me at different times of my life growing up."

Pretty Little Liars Original book cover By Sara Shepard
'Pretty Little Liars'

Hanna was the junior high version of Shepard, desperate for popularity. Emily represented when she got into swimming and found a loyal group of friends. Aria was her artsy phase, when she was "completely over the little town where I lived." And then, as Shepard puts it, "I was always Spencer." Drawing a lot from her personal life — and adding an anonymous stalker to the mix — Shepard crafted the first four Pretty Little Liars books. And then? They asked her for another four. (All in all, there have been 16 books written to date, with a new audiobook titled The Liars released this year.)

While the books gained popularity, talk of a television show — which had already been part of a development deal — increased. But the process wasn't as straightforward as fans might think. "Once we sold the books, we sold development to the WB," Morgenstein recalls. "And we stumbled through TV development a few times with a few different writers. There was a version that was YA teen but departed from the books. There was a version that was adult characters. And then finally, we wound up at ABC Family with Marlene [King] and that version was a pretty faithful version to the books, and for good reason. Because in the intervening years of stumbling around in TV development, the books became a big hit."

I. Marlene King would go on to create the popular series, titled Pretty Little Liars, which ran for seven seasons and introduced viewers to her versions of Aria (Lucy Hale), Hanna (Ashley Benson), Spencer (Troian Bellisario), Emily (Shay Mitchell), and Alison (Sasha Pieterse). The show premiered on ABC Family in 2010, and audiences quickly fell for the Liars, their chic wardrobe, and their delicious secrets.

Lucy Hale, Shay Mitchell, Ashley Benson, Sasha Pieterse, and Troian Bellisario
| Credit: Freeform

As the PLL fandom grew, so did social media. "There was such a fan base that was actually concurrent with social media starting to really take hold and have influence on the TV show," Morgenstein says. "So for us, even though Gossip Girl was a hit show and had kind of a pre-social media element to the show, Pretty Little Liars was definitely our first social media TV hit."

The series was so successful that after it ended in 2017, Freeform greenlit a spin-off series, Pretty Little Liars: The Perfectionists. But when The Perfectionists didn't garner the same popularity as the flagship series, it ended after one season.

And yet Pretty Little Liars lives on, this time in an entirely new series, Pretty Little Liars: Original Sin, coming to HBO Max this week. Much like many of PLL's antagonists, the franchise doesn't like to stay dead for long.

This time around, Riverdale showrunner Roberto Aguirre-Sacasa is teaming with his fellow Chilling Adventures of Sabrina writer Lindsay Calhoon Bring to bring fans a new story about a new group of Liars. But don't worry, they've done their research on the original. And for Bring, the project is particularly personal. "I lived right next to Warner Brothers in this little apartment for 10 years," Bring says. "Every morning I'd go out in my pajamas and I'd get the mail and there would be just dozens of tourists floating by on golf carts. Every day, I'd hear, 'Are you ready to go to Rosewood?' and cheers. So, hilariously, the gateway into PLL was living by Rosewood."

But Aguirre-Sacasa and Bring knew that they needed to bring something different to the PLL world. After all, this wasn't a remake. "One of the things Roberto and I both loved from working on Sabrina together was horror," Bring says. "I said, 'I think we should do this as a slasher show, I think A could be like Michael Myers,' and I saw the light go on in Roberto's eyes."

Photograph by Karolina Wojtasik/HBO Max Zaria, Malia Pyles, Maia Reficco, Chandler Kinney, Bailee Madison HBO MAX Pretty Little Liars: Original Sin Season 1 - Episode 3
Zaria, Malia Pyles, Maia Reficco, Chandler Kinney, and Bailee Madison on 'Pretty Little Liars: Original Sin'
| Credit: Karolina Wojtasik/HBO Max

Together, they worked to make sure they included key elements from the original series while still crafting an entirely new world. "There were so many great PLL tropes that Marlene and her writers and those actors executed. So it was a rolling conversation about how much to honor and include," Aguirre-Sacasa says. "But in creating a new group of characters, a new town, all that stuff, we also didn't feel beholden to anything."

Pretty Little Liars: Original Sin will introduce Imogen (Bailee Madison), Minnie (Malia Pyles), Noa (Maia Reficco), Tabby (Chandler Kinney), and Faran (Zaria) as they come together to face their "A," who does in fact look a lot like Michael Myers. "The production value is higher than the original series," Morgenstein says. "It all feels a little more grown up. It's a tonal departure. I think it delivers."

Although Shepard admits that "you don't expect your series to be made into a show twice," she believes there are timeless aspects to PLL that means it could live on for years to come. "There's the theme of friendship and the idea of somebody watching you and knowing stuff, which is terrifying," she says. "That's never going to go away. It's so fun that people can put their different spin on it and make it look so different and fresh and yet it still feels like it's in the Pretty Little Liars universe."

Plus, as she adds, "Everybody has secrets."

Pretty Little Liars: Original Sin premieres July 28 on HBO Max.

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Twenty years after a series of tragic events, a group of teenage girls in the town of Millwood find themselves tormented by an unknown assailant.

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