Seventeen-year-old Sutton Mercer watches from the afterlife as her long-lost twin sister, Emma Paxton, continues to pretend to be her in order to identify Sutton's killer.

The stalker's identity has finally been revealed but high school juniors Spencer, Emily, Hanna, and Aria seem condemned to repeat the past as they resume their unrepentant ways.

After high school juniors Spencer, Emily, Hanna, and Aria think they have seen Ali, their missing and presumed dead friend, they pursue clues from a mysterious stalker, trying to find out if she is still alive.

Sutton Mercer watches as her long-lost twin, Emma Paxton, takes over her identity to solve the mystery of her murder, and they end up discovering secrets about Sutton's family.

Even though the disappearance of Alison DiLaurentis has been solved, Spencer, Emily, Hanna, and Aria harbor other secrets which could interfere with their perfect lives, as they try to forget what happened to them in Jamaica last spring.

When another person that they fantasize about killing dies, Mackenzie, Ava, Caitlin, Julie, and Parker begin to wonder if they are being framed.

High school seniors Aria, Emily, Hanna, and Spencer have all have their secrets. And their stalker 'A' knows everything. A has used their secrets to torture the girls, causing them to lose boyfriends, get kicked out of school, put into jail, and constantly hounded by the press. The Girls are determined to stop A once and for all. Because everybody knows the only way for two people to keep a secret is if one of them is dead.