Deciding to come clean about a terrible mistake they committed during spring break, high school seniors Aria, Emily, Hanna, and Spencer hope to end the blackmail of a ruthless stalker who retaliates by plotting a murderous revenge.

Best friends Spencer, Aria, Emily, and Hanna find themselves under suspicion when the mysterious stranger named A tries to blame one of the girls for the death of their friend Alison and threatens to reveal the girls' darkest secrets.

Former best friends Hanna, Aria, Spencer, and Emily, who lost their best friend and leader, Alison, years ago when she disappeared, find themselves in grave danger when they pursue the truth about Alison.