When Rebecca Serle dreamed up Famous in Love, a romantic series about young actors involved in a love triangle both on an off screen, she was focused on writing contemporary fiction – not fantasy.

But all that changed when her editor Farrin Jacobs, editorial director of Little, Brown Books for Young Readers’ Poppy imprint, offered her a book-within-a-book project: Jacobs bought Serle’s three-book series about young, beautiful actors who are turning Locked, an imagined bestselling paranormal book trilogy, into a movie franchise – and she wanted Serle to write Locked, too.

But here’s another twist in this multi-layered story: until now, the connection between the two book projects has pretty much been a secret. That’s because while Famous in Love will not be published until October 21, Locked is already building a fan base. And while Serle is the author for both projects, Locked is being marketed under a pen name: Parker Witter, who is also the reclusive author character in her Famous in Love series.

Using Witter’s name, Serle wrote a prequel to Locked called “The Three of Us,” that was released in August on Wattpad, the story-sharing social platform. Starting September 15, a chapter a day became available for free on the site, and by the end of September, the entire novella will be available. Already, nearly 200,000 people have read the prequel, according to Wattpad, and more than 30,000 readers have accessed the first chapter (the book is also for sale as a $1.99 electronic book on sites including Amazon).

Now, as Famous in Love’s release date draws closer, Tina McIntyre, executive director, strategic planning and digital publisher at Little, Brown’s parent company, Hachette Book Group, said that her team is planning to treat the debut “almost like a feature film release,” including reaching out to the Locked audience using Wattpad’s unique tools. “There’s a ‘casting’ feature on Wattpad, for example, which enables readers to choose their dream cast for their favorite books,” she told PW. “We’re definitely going to do something fun with the Locked cast announcements on Wattpad!”

McIntyre said that once Famous in Love is available, she hopes the books will promote each other and share readers (while the prequel and novella are the only Locked stories written so far, book two of Famous in Love will be out in fall 2015). Because teen audiences often make such strong connections to what they read, a YA book-within-a-book project makes a lot of sense, she believes. “When readers become invested in a fictional world, they want to hang out with those characters... whether it be in novels, novellas, fan fiction, etc.”

For Serle. it’s been “really validating” to see Locked getting so many hits. “It hadn’t occurred to me to make it its own entity,” she said, though she certainly knew the fantasy’s broad strokes: in Famous in Love, newcomer Paige and Hollywood heartthrob Rainer are cast as Locked’s protagonists, August and Noah, plane crash survivors who begin falling in love after finding themselves alone on a mysterious island – that is until August’s boyfriend, Ed (played by intense Jordan), turns out to have survived, too.

But Serle found there were some challenges when it came to writing in a new genre. “Because I am a contemporary writer, it was a little bit intimidating,” she said. (Jacobs said she told her to have fun, and also remember “there needed to be an established logic for anything supernatural”). Ultimately, Serle said, it turned out to be a good experience. “I could be really inventive,” she said.

When it came to editing the project, Jacobs said she helped make sure that the two books maintained distinct voices, but also were consistent with one another. “We kept changing some of the characters’ names, so we had to be mindful of making sure that if we changed it one place, we changed it in the other,” she said. “And certain scenes are referenced in Famous in Love, so we needed to make sure those scenes existed in Locked.”

Even while Locked was, well, unlocked first, Serle said Famous in Love remains first in her own mind. “Famous in Love really drives the plot,” she said. In fact, one of the criteria she used for deciding whether to write a scene in Locked? If it would be fun to watch Paige, Rainer and Jordan film the scene in Famous in Love.