S1, E1: When their best friend mysteriously vanishes, four girls believe their secrets are safe forever. But when they begin to receive threatening messages, the truth may be only one text away. Set one year after the disappearance of Alison (series star Sasha Pieterse), the manipulative and vindictive queen bee of their group, the series revolves around four 16-year-old girlfriends — Aria (series star Lucy Hale), Spencer (series star Troian Bellisario), Hanna (series star Ashley Benson), and Emily (series star Shay Mitchell) — who have lost touch with one another until each begins to receive mysterious messages from "A," suggesting that Alison is watching them. Linked by their former bond and the panic and confusion the enigmatic messages cause, the friends are suddenly reunited, though each girl has her own secrets — secrets she wants no one else to know.