Pretty Little Liars by Sara Shepard

In a seemingly perfect suburban town, four estranged friends are drawn back together by a mysterious figure known only as "A," who threatens to reveal their darkest secrets. As they navigate the complexities of high school life, the girls grapple with the disappearance of their former leader, Alison, whose shadow looms large over their lives. Each girl harbors her own secrets, and "A" seems to know them all, manipulating their fears and desires to keep them on edge. As they try to uncover "A's" identity, they must also confront the truth about Alison and the events leading up to her vanishing, all while maintaining their facades in a world where appearances are everything.