mysterious person called "A"

Twenty years ago, a series of tragic events almost ripped the blue-collar town of Millwood apart. Now, in the present day, a group of disparate teen girls finds themselves tormented by an unknown Assailant and made to pay for the secret sin their parents committed two decades ago, as well as their own.

Based on the Pretty Little Liars series of young adult novels by Sara Shepard, the series follows the lives of four girls — Spencer, Hanna, Aria, and Emily — whose clique falls apart after the disappearance of their queen bee, Alison. One year later, they begin receiving messages from someone using the name "A" who threatens to expose their secrets — including long-hidden ones they thought only Alison knew.