The play is a youth idol TV series adapted from the novel of the same name by female writer Sara Shepard. There are many secrets hidden under the quiet appearance of Rosewood. Three years ago, the four most beautiful girls in town - Aria (Lucy Hale), Spencer (Troian Avery Bellisario), Hanna (Ashley Benson) and Emily (Shay Mitchell)'s friend, Alison (Sasha Pieterse), the most popular girl in school, suddenly disappeared. The four swore to keep the secret, but the relationship gradually drifted away. Three years later, the four received a text message from the mysterious person A, knowing the secret they had hidden for a long time, which only Alison knew. They thought A was Alison, but the police found her body in Alison's backyard, and the mysterious A was always a mystery. How will the four girls face all these changes?