The Halloween before Alison vanished finds her facing a possible usurper to her queen-bee throne. Meanwhile, Aria uncovers something surprising about her dad; and Spencer struggles with her class-election campaign as she deals with parental disapproval.

Hanna's friends want to use Caleb's computer skills to help them uncover A's identity, but Hanna is hesitant to involve him and instead throws him a surprise party. Meanwhile, Aria and Ezra face the consequences of divulging their secret romance.