Four friends—Emily, Spencer, Aria, and Hanna—keep a secret that could destroy their flawless image. And someone named “E” threatens to reveal it. Could it be their friend Alison, who disappeared three years ago? Or is it Melissa, Spencer’s older sister, whose dream is to eliminate the competition? And what about Toby, the mysterious neighbor who left town right after Alison’s disappearance? One thing is certain: any crumpled note, any strange SMS message, any threatening letter—and the girls lose everything.