Jenna notices that Alex smells differently and doesn't believe that she's talking to Spencer. She calls Toby, who puts the pieces together. He realizes that is why Spencer's horse is suddenly so afraid of her, and he realizes that when "Spencer" gave him a goodbye kiss and the book by her bedside table a couple years ago, it was really Alex. The book Alex gave Toby hasn't been read, let alone filled with Spencer's notes in the margins. Toby goes to the Liars, who weirdly believe Spencer has an evil twin right away. Mona, who has been spying on the liars, has enough information to turn redcoat. This whole time she has been working for AD to save the girls, to finally put an end to the game. She confronts Alex with the knowledge that the Liars are on to her and her loyalty is rewarded with Alex's location. Mona runs to the Liars and shares the location of where Alex is keeping Spencer and Ezra locked up.