On the night of the annual masquerade ball, the girls finally decide to put an end to A’s game. During the ball, Mona mentions to Spencer how she saw Alison spying on someone. Emily talks with her ex Paige and they decide that they’re going to attempt a friendship now that she’s out of the closet. Spencer realizes that “A” wasn’t watching Ali; Ali was watching “A”. Mona and her go back to the Lost Woods Resort, and Spencer realizes that Room One wasn’t where they had to look- it was Room two. They open the door, gasping at what they see: “A”‘s Lair. It is plastered with pictures of the girls, and other things such as the voodoo doll Alison received, the creepy baby doll costume, and a doll set, each one looking like the girls with Alison sitting on the top. Spencer finds numerous things that point to Mona being “A”, and “A” is finally revealed to be Mona Vanderwaal. She knocks Spencer out cold, and they take a drive. Aria video calls Spencer, and the girls see who “A” is. They flee to catch up with them. Spencer jumps out of the car, and the girls arrive. Mona freaks out and tries to kill Spencer, but ends up falling off a cliff. The ambulance arrives, and so does Dr. Sullivan. She tells them “A” threatened her son, which is why she left. It is then revealed Mona is alive. Meanwhile, we get a peek at what Mona is thinking while being kept in the mental hospital: She says that this is what “they” wanted, and their plan worked out just right. This means that Mona isn’t working alone. A body is found, and it is Maya’s. Emily cries while the girls comfort her.
‘A’ ending: A person in red visits Mona in her hospital room, to which she says to them “I did everything you asked me to.”