The episode begins and Hanna is sleeping in her bed when Mona sneaks in, in the middle of the night to ask for some advice. Mona’s been released from the sanatorium and is worried about re-enrolling at Rosewood High School, where she’s sure everyone will hate her. Next a person wearing a hooded sweatshirt is shown skateboarding down the street at night, being followed by an SUV. The skateboarder appears to be trying to outrun the SUV, and as the skateboarder approaches a curb the vehicle follows before slamming on the breaks and coming to a stop on the sidewalk, revealing Toby at the wheel.
With Mona out of the hospital, Emily’s parents aren’t taking any chances. Emily’s father is in her room installing a state-of-the-art security system in the house. Her father also tells her that he and Emily’s mother don’t want her out of the house at night. Meredith, the woman Aria’s father slept with, is now her substitute History teacher. Mona arrives at her locker after class, and opens it to find a cow brain stuck to her cork board using a rather large knife. Mona calmly grabs the knife and attached brain, walks to the trash can and dumps the brain in. After standing for a few seconds with just the knife in her hand, she throws that in as well; before walking over to Lucas, and whispering something in his ear. When Hanna asks Lucas what Mona said, he looks a bit worried, and then walks away.
Spencer and Aria are warring. Basically, Spencer wants to delve into the idea that Aria’s father could be connected to “A”. Emily brings up the fact that people may think they were the ones responsible for putting that brain in her locker. As the girls are discussing that they don’t feel that bad for Mona, she walks into the ladies room. The girls speak with Mona, telling her that they had nothing to do with that, and she says she believes them. After all, she helped them figure out who killed Maya. Hanna in the meantime seeks out Caleb. She noticed that Lucas was limping when he walked away from her, and she wants Caleb to find out why. When he asks why, Hanna says that the night of the Halloween dinner train, she stabbed someone in the leg with a rusty screwdriver as they were trying to throw her off the train.
Caleb agrees to do some digging. Between classes Emily sees Mona chatting with the janitor who’s cleaning out her locker. Turns out, the janitor is the same person who was acting as the front desk agent at The Lost Wood Resort, where Mona’s lair was. Spencer is eating lunch with Toby. Spencer sees Jason speaking with Mona, which irritates Spencer to no end. Back inside, Hanna and Aria have set off to the basement of the school to the janitor’s office. In the office they see that the janitor has a collection of Mona’s stuff, including her creepy doll masks. The girls manage to hide just before the janitor comes out of his office to catch them spying and he does not look happy. Hanna summons Aria to meet her at the coffee shop to discuss the creepy janitor/front desk guy apparently named Harold, being at their school.
When Aria steps out of Ezra’s apartment, she sees a gift basket by the door proclaiming “It’s A Boy” and a note, asking Aria when he’s going to start talking. After school Toby and Spencer go for a run and arrive back at Spencer’s house when Spencer spots Jason. Spencer walks across the street to speak to Jason about why he was speaking with Mona and when Spencer tries to remind him that Mona is dangerous, Jason reminds her that people used to think the same thing about him so he prefers to give people the benefit of the doubt. Spencer and Toby decide to take a dip in the hot tub, and while Spencer is stewing over Jason “not getting it,” and the fact that she’s worried about Jason because “nobody has his back” she hears something in the bushes.
When she calls out to see if anyone is out in the woods, Toby tries to get her to relax, but Spencer ultimately decides she wants to go back inside. Over at the coffee shop, Hanna, Aria, Emily, and Caleb are discussing Mona and Harold’s appearance at the school. Hanna is trying to give Mona the benefit of the doubt, while Aria and Emily are trying to remind her that Mona is bad news and not just some misguided teenager. Back at Aria’s house, she’s speaking with her dad who’s thanking her for handling Meredith being her teacher so maturely. When Aria asks what Meredith told him, he says Meredith said that Aria and her friends were “cautiously welcoming”. Then Aria asks her father what he thought of Ali. Her dad seems a little put off by the question, but gives all the right answers saying that he likes all of Aria’s friends, and that he understands that Aria still misses her.
He walks out of the room and once Aria’s attention is focused elsewhere he peeks in suspiciously. Back at Hanna’s house, she and her grandmother are watching a video that Mona posted on the Internet of Mona making a public apology. Lucas knocks on the door and Hanna pauses the video. Hanna asks him what happened to his leg, and he says that he hurt it skateboarding. Hanna starts demanding answers, and Lucas tries to stop her before telling her that, that day wasn’t Mona’s first day back, and that she’d been sneaking out of Radley for a while. Lucas then makes a hasty retreat. Later at school the girls take a peek at the janitor’s locker. The girls don’t find much in there, besides a notebook that Harold had been writing in. It appears that he’d been writing a note to Mona, thinking it was her diary; however it is actually Ali’s diary.
There’s an entry in there about Aria’s father. Apparently Ali was blackmailing Aria’s father in exchange for her silence about his relationship with Meredith. In a flashback it is shown that Aria’s father refused to give Ali the money she wanted, and she began calling Aria’s mother to break the news to her, but he grabbed her hand to stop the call. Suddenly, the girls stop reading because they hear a noise. Aria rips the final page from the diary to take with them and they run out of the office, and straight into Harold. When he asks what they were doing they make an excuse about needing to use the ladies room and finding it locked. As they try to get past him he stops Aria and grabs the paper from her hand. Just then, Toby comes down the stairs. Harold looks a little confused, while the ladies look relieved.
Toby plays innocent and walks up the stairs with the girls. As they arrive back outside, they hear screaming and see a crowd running to the starting line of the race that is taking place in the school ground. Turns out, a shed is on fire, and a woman is screaming inside. Later that night, Emily’s father is shown speaking with her about what happened back at the school. Apparently, Meredith was the woman trapped in the building. Emily’s father suggests to her that they discuss “why she won’t let him in” and that they put the fighting over Emily being allowed to go out aside. Back at Hanna’s she’s sitting down to finish watching the video. Her grandmother comes and tells her that “she’s seen enough of her [Mona] for one day”. Back at Aria’s, her father is confronting Aria about whether or not she and her friends had anything to do with hurting Meredith.
Apparently, Meredith had received a note asking her to head over to the shed. He doesn’t seem to believe that the girls had nothing to do with the accident, and Aria is just as confused as he is. Aria makes a call to Spencer, telling her that ““A” set us up” but Aria doesn’t realize her dad is listening outside the door. A hooded figure in the meantime loosens the wheels on one of the bikes at the bike rack, leading the rider to fall. The episode ends at this point.