Beneath the tranquil exterior of Rosewood Town lies a number of secrets. Three years ago, Alison (Sasha), the school's most popular girl, was friends with four of the prettiest girls in town - Aria (Lucy Hale), Spencer (Troian Avery Bellisario), Hanna (Ashley Benson) and Emily (Shay Mitchell). Pieterse suddenly disappears, and the four swear to keep it a secret but their relationship drifts apart. Three years later, the four receive a text message from mysterious person A, revealing a secret they have been hiding for a long time that only Alison knows. Thinking A is Alison, but the police find Alison's body in her backyard, and the mysterious A remains a mystery. How will the four girls face all this?