The Philadelphia Story portrayed the city's suburbs as a grand landscape of mansions and manicured lawns where the rich and idle flirt over cocktails.

In thirtysomething it was the background for a group of painfully earnest baby boomers who shared existential crises over wine coolers.

And Pretty Little Liars, the best-selling book series and TV show from Downingtown novelist Sara Shepard?

Try four teenage girls embroiled in murder, blackmail, cyberbullying and arson.

Shepard's characters, high school students in the fictional Main Line town of Rosewood, are fun, sassy girls who contend with teen pregnancy, drug abuse, madness, and sexual experimentation while solving intricate, harrowing murder mysteries. And they still manage to finish their homework.

Think of it as Nancy Drew meets Gossip Girl.

Shepard, 35, who will talk about the series as part of a family program Saturday, the final day of the annual Philadelphia Book Festival at the Free Library of Philadelphia, says she drew her characters come from her own experiences as an angsty teen at Downingtown Senior High School.

"The characters all come from aspects of my own life, things I had gone through," says Shepard, who lives with her husband, Joel Wilkens, a vintage guitar restorer and their eight-month-old son, Kristian.

So she was hit over the head with a shovel and buried alive, as happens to Alison DiLaurentis, the charismatic, manipulative, bullying, controlling girl who disappears at the beginning of the series?

Or did she go blind after being caught in a house fire accidentally set by four other girls?

Perhaps she was a championship swimmer in the making when she had to quit after becoming pregnant?

"Obviously I didn't have an affair with my high school English teacher," Shepard says, referring to another one of her characters, Aria Montgomery.

"Their stories are exaggerated. But they express certain phases I went through while growing up."

Shephard, who has written 11 novels in the series (the latest, Stunning, is due June 5), says she took those experiences, including her "rebellious punk phase" and married them to her lifelong fascination with murder mysteries to come up with the first Pretty Little Liars installment in 2005.

The story, about four girls who investigate the disappearance and murder of their friend Alison, anticipated what was to become a major concern for parents and teens with its exploration of cyberbullying.

"It was 2005 and text messaging was just becoming popular and cyberbullying, the idea of it, was just coming along," says Shepard. "I had no idea it was going to be such a phenomenon."

Both the books and, regrettably the bullying, are huge cultural phenomena.

Shepard's projected four-book series grew to eight, then 10. "I'm on number 12 now. We'll stop at 14," she says. "I'm pretty sure."

In June 2010, ABC Family jumped on the series' success, debuting a TV adaptation starring Troian Bellisario, Ashley Benson, Lucy Hale and Shay Mitchell. The show's third season will premiere on June 5.

Show creator and executive producer I. Marlene King says a TV version was inevitable.

"The world that Sara created and the characters who inhabit it was just so ripe for translation for TV. It was impossible not to consider it," says King, who says she inhaled the first book in the series in one sitting. It's a winning premise, she says, combining as it does "this involved murder mystery with a touch of Gossip Girl deliciousness and heightened reality."

King says the show tries to stay true to the books, while coming up with slightly different mysteries so both reader and viewers will continue to be surprised.

Pretty Little Liars' mix of earnestness — it deals with some pretty heavy issues — along with its glossy, decadent feel and dark, gothic undertones seems irresistible to young fans.

"What is remarkable to me is that girls who fall into the reluctant reader category get sucked into this stuff," says book festival organizer Andy Kahan. "That's what happened with my daughter [13-year-old Kiara] who was always more a Facebook reader than a book reader."

Atlantic City High School freshman Abby Anmuth, 15, says she got hooked into the story through the TV show. Each episode, she says, ends with a gripping cliff-hanger. "I thought it was so creepy" at first, "but it really grabs you and makes you want to watch the next episode even if you don't want to."

Jamie Primeau, 21, a junior at the College of New Jersey in Ewing, is also a fan of the TV version. She says she likes the story's Byzantine plot lines and never-ending twists. "Each episode gives you enough information to make you think you can solve the murder," she says. "But then you get thrown a real curve ball and you can't wait to see the next one."

Wynnewood's Sylvia Coopersmith, 13, says she digs that the show stays true to the books' authentic Philly-area settings. "I love that all the characters live right around here. I can picture all this stuff happening in my own school," she says.

"Well," adds Coopersmith after a pause, "probably not the murder."

Contact staff writer Tirdad Derakhshani at 215-854-2736 or tirdad@phillynews.com

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