Emily, Hanna, Aria and Spencer formed an alliance with Mona to break into Radley and Spencer was a arrested for the murder of Bethany Young in Pretty Little Liars’ Fatal Finale, “Taking This One to the Grave.”

Pretty Little Liars’ summer finale began on Thanksgiving day, with Aria (Lucy Hale), Ezra (Ian Harding), Hanna (Ashley Benson) and Emily (Shay Mitchell) standing on the street in front of a house where they had just discovered a dead body. Somebody has been murdered – there was blood in the house. Before the police begin questioning them, they receive texts from A: “It’s all your fault.”

Ali Is 'A'

Cut to 36 hours earlier, Ali (Sasha Pieterse) sits in a police interrogation room getting ready for a polygraph. Detective Holbrook (Sean Faris) stands behind the glass, and, curiously, when asked whether they should be waiting for Detective Tanner, Holbrook does not respond. (Could Holbrook be working with Ali?) After realizing that Ali was going to the cops, Spencer, Emily, Hanna and Aria head over to Mona’s house to ask for her help. Mona (Janel Parrish) was right when she told Aria that Ali would get bored with her and move on to target them, and they need her help. They tell Mona that Ali is talking to the police, and Mona says she’ll do what she can. After the girls leave, Mona calls Lucas (Brendan Robinson), telling him they’re at “Code A.”

When Mona meets Lucas for their anti-Ali army meeting, she is surprised to find that he’s the only one who showed up. The rest of Mona’s army has been swayed by Ali’s seductive ways, and now it’s just them. Thus, a tentative alliance between Mona and the girls is born. In the bathroom at Rosewood High, the five girls meet up and establish that Ali is A, and Mona wants to help them because she just got early acceptance letters from colleges and she’s going to need friends to survive senior year.

Ali’s a sociopath, says Mona, and she curated the girls to torture them. Spencer is smart, Emily is loyal, Hanna is the admirer and Aria is compassionate. But now that they’ve abandoned her, Ali is pissed, and she’s gone to the police to end the ‘A’ game. Mona gives them strict instructions not to tell their “bed buddies” about their plans and the group scatters when the twins Ali poached from Mona’s army walk in together.

Paige (Lindsey Shaw) and Emily kiss and make up and start decorating Emily’s house for Christmas – a Fields tradition – after school. Hanna and Caleb (Tyler Blackburn) join them while Aria goes to Ezra’s to help him bake pumpkin pie. Her mother invited Ezra over for Thanksgiving. It’s a test, she says, to see if he’s worth a second chance. And Spencer (Troian Bellisario) gets a visit from new police officer Toby (Keegan Allen), dressed in his uniform. She gives him his graduation present: a pocket watch with an inscription that reads, “You are my once upon a time… – S.” The two make plans to go to his Police Academy graduation later that night.

Mona And Spencer Break Into Radley

Meanwhile, Lucas and Mona hack into the Rosewood PD and download a copy of Ali’s interview, finding that the police are clearly less interested in Ali as a suspect than Spencer. They theorize that Spencer killed Bethany Young to keep Ali from telling anybody that she was taking pills, and Ali doesn’t exactly contradict that line of thinking. After hearing the tape, Spencer is, naturally, freaked, and at first she tells the girls that they shouldn’t go forward. They should just wait, and her mother will help her when the time comes. Then, Caleb, who knew Hanna was keeping something from him, shows up with some bad news: the police are no longer interested in Ali as a suspect in Bethany Young’s murder, they are completely focused on Spencer. But, the police theory doesn’t make sense: why would Spencer kill Bethany Young to get on Ali’s good side? The group now has a new plan: break into Radley and steal Bethany Young’s records to find the connection between Ali and Bethany.

Mona and Spencer do the breaking and entering, dressing up as nurses and sneaking into the file room while Aria distracts the main nurse by dropping paint in her art class and Hanna and Caleb keep tabs from outside. Things go smoothly until Detective Holbrook shows up and begins asking questions. Specifically, he corners Aria in the art room and asks her if she started volunteering there after they identified Bethany Young’s body. Hiding from the Detective in Hanna’s car, Caleb finds a list of colleges that appear to be way out of Hanna’s league, and Hanna reveals that she’s secretly a genius and got a crazy good score on her SATs.

Ali Wanted Bethany Young Dead

Mona and Spencer manage to get away without Holbrook seeing them, and they take tape recordings of Bethany Young’s therapy sessions with them. Going through the tapes, they find a connection: Mrs. DiLaurentis had an affair with Bethany’s father, which was supposedly why she was visiting Bethany at Radley. In the recordings, Bethany wonders if she can trust Ali, or if the girl is just like her mother.

Emily is on Ali duty and invited her over to ‘talk’ as a distraction. Ali quickly figures out that Emily is lying to her, but she doesn’t answer when Emily asks her if she’s ‘A.’ She walks out of Emily’s house just as Paige is arriving, but doesn’t see her. When Paige sees Ali get in a car with the twins on her ‘A’ team, she ditches her plans to see Emily and follows them.

Spencer Is Arrested, Mona Dies

Spencer called Toby after leaving Radley and heard him get into a car crash over the phone. Toby escaped with a broken leg, and he’s going to be out of commission for a little while, but, he is expected to make a full recovery, and is checked out of the hospital on Thanksgiving Day, just in time to watch Spencer get arrested at The Brew.

As the cops carry Spencer away in handcuffs, Mona is still studying the tapes she stole from Radley. She calls Aria, who’s at home with Ezra, with some big news: Ali wanted Bethany dead because she knew about her mother’s affair and was jealous. She knows that Ali is ‘A’ and she can prove it. Just as she gets off the phone, a figure with blonde hair, wearing a hoodie, sneaks up behind her.

Aria, Ezra, Hanna and Emily rush over to Mona’s house to find out what she’s discovered, but they’re too late. The house is completely trashed, and there’s blood everywhere. When Detective Holbrook addresses the press, he tells them that they have not found a body, but there is so much blood in the house that they declare Mona’s death a homicide. The girls cry in the street, and Ali watches, completely emotionless.

The episode ends with A replacing baby Jesus with a Mona doll in the nativity scene outside Emily’s house. A takes the Jesus doll and gently places it in the trunk of a car next to Mona’s very dead body.

Mona fans, fear not, Janel Parrish has promised that she will return to Rosewood in flashbacks.

Pretty Little Liars will return with a Halloween special on Tuesday, Oct. 21 at 8 p.m. on ABC Family.