The Halloween before Alison disappeared faces a possible usurper to his throne queen. Meanwhile, Aria discovers something surprising about her father, and Spencer-class struggle with the election campaign as she deals with parental disapproval.
The series follows the life of Aria Montgomery (Lucy Hale), Spencer Hastings (Troy Bellisario), Hanna Marin (Ashley Benson) and Emily Fields (Shay Mitchell), four girls whose clique falls apart after the disappearance of their queen bee, DiLaurentis Alison (Sasha Pieterse). A year later, they begin to receive messages from a mysterious figure with the name "A", who knows his secret. At first they think it's Alison herself, but after she is found dead, the girls realize that someone else knows their secrets - including long-hidden those who thought that only Alison knew.