A summer has passed since Aria, Emily, Hanna and Spencer found out about Mona being "A" and Maya's death. With the terror seemingly over and an alleged murderer now behind bars, the town of Rosewood is slowly healing from old and new wounds and trying to get back to normalcy. Each of the four girls spent their summer in different ways - Aria taking a photography class, Spencer taking college courses at Hollis, Hanna taking cooking classes with Caleb and Emily building houses in Haiti.
A new "A" player is in town and is determined to show the Liars that he/she means business. After getting a gruesome reminder that "A" is still calling the shots, Aria, Emily, Hanna and Spencer try to quickly devise a plan on how to deal with this old/new threat and the usual game that has been taken up a notch. Spencer and Hanna continue to play with fire as they look for answers, while one of Aria's past indiscretions becomes fodder for "A's" game.
With Spencer's mom now taking Garrett on as a client, Spencer is sure that there is a reason forcing her mother to take on the case. But when she starts questioning, she doesn't so much learn why her mother took the case as stumble upon a larger Hastings secret. Emily also gets some surprising news about her English exam and fears what those consequences could hold.
The truth can sometimes hurt and the Liars must take that into account when deciding to reveal secrets. Hanna's visits with Mona are driving a wedge between Hanna and Caleb. But would it be so bad if Hanna told Caleb that she needed to see Mona to get information about this "A?" Aria, on the other hand, is dreading telling Ella that Byron is back in the dating scene and dating Meredith. But wouldn't it be better if Ella found out from Aria than hearing it someplace else? And Spencer needs to know the truth about Melissa, even if the truth hurts.
Jenna's extravagant birthday party seems to be too good to be true and Aria, Emily, Hanna and Spencer think something else might be up - especially when it turns out that Garrett is getting a pass out of jail to visit his ailing mother on the same night. The timing can't just be a coincidence; the Liars are convinced it all has to do something with "A." With Emily getting an insiders' view working the party, Aria working the crowd as a party-goer and Spencer staked out at the hospital, what could go wrong? The answer is - everything.
After getting a major clue from Garrett, Hanna and Spencer set out on their separate missions. Hanna sees a perfect opportunity to catch "A" or to at least see who is helping Garrett out. But her perfect plan starts to quickly unravel, leaving Hanna frustrated and desperate. Spencer tries to figure out the meaning of the clue and enlists Jason's help in the search.
Meanwhile, Emily gets another flashback from "that night" which leads her to a surprising suspect and Aria starts to question Ezra's sudden influx of cash.
With new key evidence in Alison's murder case, Hanna fears that "A" may be framing her after a visit from Det. Wilden. With paranoia setting in, Aria decides that she has to turn to Mona for answers if she is going to help Hanna. But is Aria ready to face her former tormentor, and more to the point, is Mona ready to give Aria the answers the PLLs are desperately looking for? Meanwhile, someone from Ali and Jason's past arrives in Rosewood and piques the girls' interest.
Emily is struggling to deal not only with the loss of Maya, but the knowledge that someone drugged her "that night" and how that has now affected Paige. Going to make amends with Paige and try to explain the drugged flask ends up leading Emily to more insight of what she did "that night." Also trying to help Emily out, Spencer turns to Caleb to help crack into a website that might hold answers for them all.
Meanwhile, Aria realizes she knows very little about Ezra after meeting his mother and Hanna makes a plea on Mona's behalf.
Spencer and Aria find themselves at the Kahn brothers' party in hopes of saving Spencer's college career. What originally was going to be a quick stop by to ask a favor of CeCe's friend turns into an opportunity for Aria and Spencer to get some answers from Jenna with a heated game of "Truth." But will Aria and Spencer be willing to give up some of their "truths" to get the answers they are looking for?
Hanna and Emily try to figure out clues about Maya at the Kahns' cabin in the woods. Meanwhile, Spencer investigates Noel; and Aria tries to understand what she's learned about Ezra's background.
Spencer finds out Paige's violent past with Alison and warns Emily about her, but Emily is weary to take her advice. Meanwhile, Aria tries to help Ezra put his past behind him, but this ends up being more difficult than she anticipated.
Maya's trial gets underway, and Emily can't stand the media attention. "A" then extends a branch to the girls, who are skeptical; and someone close to the girls betrays them.
Aria, Emily, Hanna and Spencer are looking forward to some good old Halloween fun now that the traumatic events with Nate are behind them. But once aboard the Rosewood Ghost Train, the girls are in for much more than just some childish trick or treats. With "A" running amuck and unexpected party-goers popping up at every turn, this Halloween event becomes one killer party.
Radley Sanitarium has given Mona a clean bill of health and she is headed back to the halls of Rosewood High, much to the Liars' dismay. With their former tormentor now back in their everyday life, Aria, Emily, Hanna and Spencer take very different views of the "new" Mona. She made their lives a living hell... Is she really cured? And what other secrets could she be holding onto? It's up to Mona to prove to the Liars if she has changed or not.
After the shocking events at the school marathon, Aria, Emily and Spencer are sure now more than ever that Mona is up to her old tricks. Hanna, still holding out hope for her former friend, is not so sure. With Mona seemingly popping up everywhere, it sure seems like she has a plan. But with no real evidence to prove Mona is back to her evil ways, how can the Liars prove what they believe to be true?
Meanwhile, Aria's fears about her father grow stronger when something vital that is hidden in her room goes missing.
Aria is down for the count when sidelined by the flu, so Hanna and Emily are on their own to follow up on a new clue. Surprisingly, Meredith steps up to help take care of Aria while her father is away, but when it starts to look like Meredith may have ulterior motives to her nursing Aria back to health, Hanna and Emily turn their attention towards saving their friend. Is Meredith just trying to start anew with Aria and be her number one fan, or is there reason for her friends to be concerned?
Aria, Emily, Hanna and Spencer have more than most, but with all of the secrets they are holding it may be starting to get overwhelming for them. Aria knows that she should tell Ezra about his son, but she isn't ready to face the idea of what it might do to her relationship. Hanna, on the other hand, is sure Caleb is keeping a secret from her and she is determined to find out what it is. Spencer is fed up with all of the secrets and decides she no longer wants to play the games. Will their secrets drive the girls to take desperate actions that could, in turn, make the situation worse?
Now that Ali's remains are back with her family, the DiLaurentis' are set to bury her again, giving Aria, Emily, Hanna and Spencer another opportunity to say goodbye to their friend. With everything that has gone on since Ali's disappearance, the girls are divided about going to yet another memorial. Aria, Hanna and Emily are ready for another round of goodbye, if not for them but to also support Jason. Spencer, on the other hand, has had enough and wants nothing to do with the burial. Why keep saying farewell to a girl who wasn't that great of a friend after all?
When dealing with matters of the heart, people react in many different ways: Still crushed over her break-up, Spencer continues her downward spiral as she now takes her anger and hurt out on Mona. Caleb, on the other hand, hides his pain by being closed off when discussing his father. But when Hanna devises a plan to bring father and son back together, will that help Caleb heal old wounds or just make things harder? And Aria, who is still missing Ezra, finds she is spending more time with Wes.
Meanwhile, Emily and Jason work together to put together the pieces of Ali's trip to Cape May and what really happened during that vacation.
Shaken up after recent events and holding new information about Det. Wilden, Aria, Emily and Hanna are on the hunt for answers about the detective's past. Looking to Shana and Cece for more insight, the ladies seem to be making progress in their search. But they quickly start running out of time when they learn that Wilden is close on their heels and determined to stop them. Now with Det. Wilden on the war path, some residents of Rosewood will find out how far he is willing to go to keep his secrets from coming out.
Spencer is finally ready to talk, but Emily is not so ready to accept what she has to say. Will she heed Spencer's warnings or will Emily go off to find her own answers down a path "A" has designed for her? Hanna, on the other hand, is preoccupied with helping her mother after Ashley is involved in a hit-n-run accident. Now having a new secret to hide, Hanna wonders if "A" had something to do with it after all. With Aria, Emily, Hanna and Spencer are now really afraid does "A" have them right where they want them?
Spencer hasn't been herself lately, but has she had enough to just disappear? Could "A" have done something to her? These are all questions that Aria, Emily and Hanna are asking themselves when Spencer goes missing. But when it turns out even her family doesn't know where Spencer has gone to, the girls frantically search for answers hoping their worst fears aren't true. But where Spencer does turn up at, maybe she doesn't want to be found.
Meanwhile, Emily gets the surprise of a lifetime when she meets Gold Medalist Missy Franklin.
As "A" continues to play games, the stakes are raised higher as each girl is forced into difficult positions. Aria starts to seriously contemplate her relationship with Ezra as his new family situation continues to eat away at her. Hanna is thrown into the middle of Caleb's family drama when Jamie's shady past comes back to haunt him. Emily is determined to prove Spencer wrong in hopes of helping her, but she might not be ready for what she finds. In the end, will the Liars be able to get out of their sticky situations or will "A" have them right where he/she wants them?
Meanwhile, Spencer searches for answers about Mona's time in Radley Sanitarium.
Spencer is back home and presenting a good front, but Aria, Hanna and Emily are not so sure their friend is fully back after seeing how fragile she was just a day or so before. Unfortunately the girls don't have much time to ponder Spencer's health as shocking revelations are brought to the forefront. With so much happening and new information being uncovered, will the Liars be ready for what is waiting for them?