Mona gets a special visit at Radley from Toby as she prepares for her favorite holiday: Halloween! Meanwhile, the Liars celebrate Halloween by boarding the Ghost Train, which they learn is full of tricks and treats. The ride starts out fun with performances by special guest star Adam Lambert, but things go dark as Garrett reveals secrets about Alison to Spencer. Caleb surprises Hanna with a surprise appearance, and Paige saves Spencer from a mysterious attacker. Later, Aria is captured by a masked villain and wakes up next to a very dead Garrett. When the police arrive on the scene, Ali's body is found hidden on the train!