For a “pretty little” series, Pretty Little Liars is generating some pretty big sales. And that’s even before June 8, when HarperCollins publishes Wanted, the final title in the eight-book series—and ABC Family launches the first of 10 hour-long episodes of a TV show based on the racy teen murder-mystery tale.

HarperCollins, which has sold more than 1 million copies of the first seven books, is printing 150,000 copies of Wanted and is reissuing 100,000 copies of book one with a new cover. It features the 20-something television actresses who are portraying the wealthy 16-year-olds in Sara Shepard’s story. And HarperCollins will give the first four books with the original cover—doll replicas of Pretty Little Liars’ female leads—a banner that touts the TV show. (The original 10 TV episodes just cover the material in the first four titles.)

“We try to see this happen with all our properties that cross over—to really get the publishers and the television network or film studio working together,” says Leslie Morgenstein, CEO of Alloy Entertainment, which develops, creates, and produces such books, films, and TV shows as Gossip Girl, Vampire Diaries, and now Pretty Little Liars.

Pretty Little Liars was born after someone at Alloy asked, “What’s a teen Desperate Housewives?” says Morgenstein. “We looked at what the property was and broke it apart. It was a murder mystery with a soap.” So is Pretty Little Liars, set three years after queen bee Alison vanishes during a slumber party.

Alloy wrote an in-house treatment and then chose Shepard, one of its ghost writers, to be the named author. “The majority of our properties do start with the book first,” says Morgenstein. Alloy and Shepard developed a partial manuscript before going to HarperCollins for the book and Warner Brothers for TV development. “You have a whole bunch of different editors thinking about how to make the story better,” says Shepard. “It is definitely a team.”

The team produced a mystery that keeps girls up late with their flashlights. Each twist-filled chapter tells the story of one of four different secret-keeping girls at an elite private school on the Main Line, in suburban Philadelphia. Shepard herself grew up in Downingtown, Pa., where she lives today with her husband, who restores vintage guitars. Ironically, she has never watched Desperate Housewives—though her series also features crimes and taboos in a seemingly perfect suburb.

Characters deal with issues such as drinking, smoking, sex, bulimia, sexual orientation, plagiarism, student-teacher romance, and shoplifting. Yet the books and TV show are rated PG. “Some of our characters have sex, but you don’t see it,” says Morgenstein. “You assume at some points they’re drinking alcohol, but you don’t see beer bottles.” Similarly, Shepard leaves out graphic sex scenes.

Shepard doesn't glamorize the girls behaving badly. Indeed, the books—which span six months during the girls’ junior year of high school—can be read as cautionary tales. “Any of the scenes where the girls are drinking, nothing good ever happens,” says Shepard. “I try to make them change and learn to be better people and not be so obsessed with how they look or how they’re acting.”

According to the current editor of the series, Farrin Jacobs, young readers can live vicariously through the books. “You’re watching people do something you would never do,” says Jacobs, who is also editor of Anna Godbersen’s Luxe series and co-editor of Lauren Conrad’s books. “It’s fun to see something happen to them. There are a lot of consequences in these books. It’s definitely ‘peel back a veneer on the perfect life and look what lurks beneath that.’ ”

Word of mouth helped the series catch on with teens. “The kids started telling each other about it,” says Katherine Fergason, manager of Bunch of Grapes Bookstore in Vineyard Haven, Mass. Like other “guilty pleasures,” it sells best in the summer, she says. Often middle-school girls graduate from the Clique series to this one, says Karlene Rearick, owner of The Alphabet Garden in Cheshire, Conn. “I think sometimes people tend to think this type of book is for mean girls. [But] the girls who have read it are like, ‘oh, no, it’s like school.’ ”

Girls also like figuring out which cover art “doll” is which girl. The books aren’t numbered, and the dolls aren’t named. For the record, the doll on book one, with a yellow cover, is Spencer. The orange cover is Hannah, pink is Aria, and green is Emily. “The code has been cracked!” jokes Shepard.

To write the series, Shepard consulted her childhood journals. “I would re-read them a lot and just kind of see what I was thinking and what mattered a lot,” she says. Growing up, she was most like Pretty Little Liars’ artsy Aria, she says. (In high school, she wore Doc Martens and striped stockings and dated a boy with an ancient VW Bug.) But she also had a Hannah-like, sticky-fingers experience. When she was in seventh grade, she took “pointless things” such as nail polish, she says. While filching socks at Urban Outfitters, alarms went off and employees took her photo and told her never to return to the store. “It scared me from ever stealing again,” she says.

Today she is busy writing a new four-title, two-book-a-year series, which debuts next January with The Lying Game. In the series, long-lost twin sisters are separated at birth; the narrator is the dead twin, who wants to solve her murder through following her sister. “The world is a little less glamorous than Pretty Little Liars,” says Shepard. “There is still the rich girl and the beautiful, captive boys. And everybody kind of has a secret, and they’re all vulnerable.”

In her spare time, Shepard writes adult books. In 2009, she came out with The Visibles. A second adult book, circulating with U.S. editors now, is coming out in the U.K. under the name Everything We Ever Wanted.

Shepard is no Carolyn Keene (Nancy Drew creator Edward Stratemeyer wrote outlines for a stable of ghost writers, led by original author Mildred Wirt Benson). She uses her real name and writes the entire series—albeit with substantial input from Alloy and HarperCollins. “It’s in no way book-factory-making. She’s so much a part of why this series is working,” says Jacobs, her editor.

The author has a strong online presence, and she is currently tweeting the first chapter of book eight—a tradition she began with book six, Killer. “She is a bright, articulate person who can get out there and be a very active promoter of the books,” says Morgenstein. “She is a great champion of the series. When you have a pseudonym, you don’t have the consistency of the writing, and you don’t have the person who’s out there.”

Shepard is definitely out there. On June 5, she and the stars of the ABC Family show are doing an event at The Grove in Los Angeles, just before the show's June 8 premiere. Morgan Eisenstein, 13, of suburban Chicago, already plans to watch it at home with a few fellow Pretty Little Liars fans. “It’s always really intense,” she says.

ABC Family executives hope to make the TV show, like the books, “addictive,” says Mina Lefevre, v-p of programming and development for ABC Family. “You have a new world that you’re introducing to new viewers—and you’re adding twists and turns for the fans of the book that they didn’t expect.” Her goal: “We want to fulfill the relatability, the teen emotional connection of the girls’ friendship, but also give you the thrill ride that I got when I was reading the books.”

Like Shepard’s younger fans, Lefevre is looking forward to the final book. In it, Shepard says, “all the loose ends will be tied up.” But it won’t necessarily be the absolute end of the franchise. “We are thinking about doing a diary, an Alison’s diary,” says Shepard. Undoubtedly, it will be the diary of a not-so-wimpy kid.