If the Twitterverse is quieter than usual today, you can blame (or thank) Kiera Cass, author of The Selection series. Her many fans will be busy reading The One (HarperTeen), the final volume in her saga about working-class girl America Singer and the men she must choose between.

Social media-savvy fans were whipped into a frenzy of anticipation this past weekend by HarperTeen’s promise to “unlock” the first 10 chapters in advance of the release date if enough readers used the hashtag #unlocktheone on Twitter, Tumblr, or Instagram. More than 300,000 fans did so, in less than 48 hours, with #unlocktheone trending in the U.S., Brazil, and the Philippines.

On Facebook fan page for the series, readers reacted to the sneak peek: “Nothing is better than waiting desperately, refreshing web page every hour or so and to see what percentage of the next chapter has been unlocked,” wrote one reader. “Chapter 10 was just perfect,” wrote another. “I can’t wait anymore!!”

“I’m kind of speechless,” said Cass, who is slightly flabbergasted by almost every aspect of her trilogy’s success: The fan who came to a signing carrying a copy of The Selection festooned with a thick fringe of post-it notes on which she had written dozens of questions. The 900 readers in line for Cass’s autograph at an event in Sao Paolo, Brazil. (“I think I posed with every single one of them for a selfie, too,” she recalled.) The security guards in the Philippines who stood with their arms linked to hold back fans, so that Cass could get into a bookstore where she was scheduled to appear.

“I was like, ‘They do realize, it’s just me, right? Not a band or a movie star?’ ” she said. “If you see footage of me entering the store, you can see I’m crying. It was so overwhelming.”

Cass, who lives in a rural corner of southwestern Virginia with her husband and two young children, tried on several hats before settling into being a novelist. She started college as a musical theater major, but switched universities, and majors, twice. She wound up getting a degree in history from Radford University in 2003 because she was able to complete the requirements for it without having to take a lot more courses.

“Theatre, music, history,” she said. “It was all one kind of storytelling or another.”

She had written one self-published novel, Siren, in 2009, when two well-known stories “merged in my head.” One was Cinderella, who Cass decided had gotten more than she bargained for when she asked her fairy godmother for a dress and a night off, and wound up with a husband. The other was the biblical story of Esther, a poor orphan, who was among the many beautiful virgins summoned to the palace for a year’s worth of grooming as part of the king’s search for a new queen.

“She’s portrayed as a heroine because she saves her people, but I couldn’t help but wonder if maybe Esther was not really interested in being queen,” Cass said. “What if she was already in love with the boy next door? At that point, I knew I wanted to write a story about a girl who came from a humble background and gained the attention of a prince, but wouldn’t want him because she was already in love.”

The first book, The Selection, pitched alternately as “The Hunger Games in ballgowns,” or as “The Hunger Games meets The Bachelor,” was an instant hit with readers, vaulting onto the bestseller list. A second volume, The Elite, was published in 2013. Together, the first two books have sold more than 800,000 copies. They also briefly garnered Hollywood’s attention – the CW made two pilots before deciding not to commit to a full series.

HarperTeen announced a first printing for The One of 300,000 copies in the U.S.; the books have also made a substantial splash overseas, with rights sold into 26 territories. “The fact that it’s all over the globe, that you can pick up a copy of my book written in Chinese, is still a little unbelievable to me,” Cass said.

The author credits the jacket covers, designed by Erin Fitzsimmons and Alison Donalty, and photographed by Gustavo Marx, with helping the books find an audience. “They hit it out of the park on the first try,” she said about The Selection cover, featuring a model – Audrey Hollister – portraying America in a ruffled blue ballgown. “People are always asking me, ‘Where can I get that dress?’ but the first one was vintage, so I couldn’t help them there.” The white gown on the cover of The One, however, is a wedding dress designed by Pnina Tornai, whose gowns have appeared on TLC’s Say Yes to the Dress. “So if you want to get married in that dress, you can,” Cass said. (The price for it at Kleinfeld Bridal, which carries Tornai’s line in the U.S., is listed as in the “$10,000-up” range.)

One measure of just how effective the covers are, Cass says, is that very few of the foreign publishers have changed the artwork. She has only seen one different version – an Indonesian cover that features a cartoon drawing of her heroine wearing jeans, looking into a mirror. “It’s super cute, but almost all of the other editions have the same photographs” as the U.S. editions.

Cass, who turns 33 later this month, will celebrate her birthday on the road, crisscrossing the country to visit bookstores and making stops at the Romantic Times Convention in New Orleans and BEA.

One question Cass always gets is whether she’s Team Maxon or Team Aspen – meaning, is she rooting for America to wind up with the prince or the commoner? She knows this time around she’s also going to get asked repeatedly if America’s story is really done. “Everybody is already asking if I’m going to keep the story going, but as of this point, I’m working on something else,” Cass said.

She’s also made herself a vow not to read replies on her Twitter account, at least not for a while. “The end is coming. Not everybody’s going to be happy.”