Pretty Little Liars Series by Sara Shepard

Three years ago, Alison disappeared after a slumber party, not to be seen since. Her friends at the elite Pennsylvania school mourned her, but they also breathed secret sighs of relief. Each of them guarded a secret that only Alison had known. Now they have other dirty little secrets, secrets that could sink them in their gossip-hungry world. When each of them begins receiving anonymous emails and text messages, panic sets in... moreThree years ago, Alison disappeared after a slumber party, not to be seen since. Her friends at the elite Pennsylvania school mourned her, but they also breathed secret sighs of relief. Each of them guarded a secret that only Alison had known. Now they have other dirty little secrets, secrets that could sink them in their gossip-hungry world. When each of them begins receiving anonymous emails and text messages, panic sets in. Are they being betrayed by some one in their circle? Worse yet: Is Alison back? A strong launch for a suspenseful series. less

In idyllic Rosewood, Pennsylvania, four very pretty girls just can't help but be bad. . . .Hanna will do anything to be Rosewood's queen bee. Spencer's digging up her family's secrets. Emily can't stop thinking about her new boyfriend. And Aria approves a little too strongly of her mom's taste in men.Now that Ali's killer is finally behind bars, the girls think they're safe. But those who forget the past are condemned to repeat it. And they should know by now that I'm always watching. . . .