Four friends band together against an anonymous follower who threatens to reveal their darkest secrets, while unraveling the mystery of the murder of their best friend.
A summer has passed since Aria, Emily, Hanna and Spencer found out about Mona being ‘A’ and Maya’s death…. 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. But… with post-traumatic stress, anger and the acquisition of more secrets the four Liars are anything but fine. Now all back together and coming upon the second anniversary of Alison’s disappearance, the girls find themselves back on the defensive when a shocking event rocks Rosewood.
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.
Meanwhile, a still very shaky Emily tries to focus on school but could easily be derailed when she remembers a crucial piece from "that night."
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.
Meanwhile, Aria agrees to be Jenna's accompanist in order to keep tabs on her, and Hanna tries to reach out to Lucas.
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.
Meanwhile, Emily finds some solace after meeting Maya's cousin, Nathan.
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.
Meanwhile, Hanna's wallowing through heartbreak leads her to a shocking discovery.
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?
Meanwhile, Hanna gets another text from "A" about Caleb.
After learning that Noel and his family's cabin had something to do with "that night" and possibly Maya's disappearance, the girls work to try and put the pieces together. Hanna and Emily head out to the Kahn family cabin looking for clues linking Maya to the site, while Spencer does some snooping of her own on Noel. Could Noel have had a hand in this after all, or are he and Jenna just bluffing to send Aria, Emily, Hanna and Spencer down the wrong path?
Meanwhile, Aria must deal with the aftermath of meeting Ezra's mom and the information about Ezra's past.
Emily's relationship with Paige has been anything but easy, but she finally feels like their relationship is going in the right direction. So when Spencer comes to her with a sordid tale about Paige's history with Alison, Emily is not ready to heed her friend's warnings. With Spencer knowing Paige's violent past and this new information about a blood feud between Alison and Paige right before Alison disappeared, she can't stand by to let one of her best friends get close to a potential enemy. But will Spencer cross a line that Emily can't forgive in her attempt to prove to Emily who Paige really is?
Meanwhile, Aria feels she has to help Ezra move on from his past if their relationship is to move forward, but what she finds may be more than she expected.
In the midseason finale, Emily is caught in the crossfire as Maya's murderer is revealed and the girls are betrayed by someone close to them.
Trick or treat? The Rosewood Halloween Ghost Train becomes one killer party in this special Halloween-themed episode. Plus, Adam Lambert performs.
Radley Sanitarium has given Mona a clean bill of health and she is headed back to Rosewood High, much to the girls' dismay. Could their former tormentor really be cured?
Aria, Emily, Hanna and Spencer are sure that Mona is up to her old tricks again, but can they prove it? Meanwhile, Aria's fears about her father grow stronger.
Meredith (AMANDA SCHULL) helps take care of Aria when she is sick - but could Meredith have ulterior motives? Spencer surprises Toby (KEEGAN ALLEN) for their anniversary.
Will their secrets drive the girls to take desperate actions that could make things worse? Plus, Emily learns more about what Ali may have been hiding the summer before her murder.
Alison's family is set to bury her again, now that they have her remains, but the girls are divided about going to yet another memorial. Emily visits Dr. Sullivan (ANNABETH GISH).
Spencer takes her anger and hurt over her breakup out on Mona. Aria finds she is spending more time with Wes (GREGG SULKIN). Emily and Jason (DREW VAN ACKER) work together.
Holding new information about Detective Wilden (BRYCE JOHNSON), Aria, Emily and Hanna are on the hunt for answers about the detective's past. Spencer finds someone to lean on.
Spencer is now ready to talk, but Emily is not ready to accept what she has to say. Hanna helps her mother and keeps a new secret, and wonders if "A" had something to do with it.
Aria, Emily and Hanna try to locate a missing Spencer - but Spencer may not want to be found. Emily meets Olympic gold medalist MISSY FRANKLIN (guest starring as herself).
"A" plays games with higher stakes. Aria considers things with Ezra and Hanna is thrown in the midst of Caleb's family drama. Spencer looks for answers about Mona's time in Radley.