In the season four premiere, the Liars are desperate to uncover what new scheme "A" has in store for them in the wake of the lodge fire, and have no choice but to turn to Mona for answers, now that she is also being targeted. Aria struggles with seeing Ezra in the wake of their breakup, and Emily starts to make plans for life after high school. Meanwhile, "A" sets Toby on a new path, what's in the trunk is revealed, and a shocking discovery reverberates through Rosewood.

Hanna worries that her mother is keeping a dangerous secret and is determined to protect her at all costs, which leads her to an uncomfortable meeting with Detective Holbrook. A clue in Ali's things leads the Liars to a creepy mask maker, who takes a shine to Emily and may have ties to another Rosewood resident. Spencer and Toby continue their search into a painful chapter of Toby's past and Melissa returns to Rosewood. Meanwhile, A targets Emily's mom, leading Aria to make a desperate plea of Ella.

Holbrook's partner, Lt. Tanner, comes to town, intensifying their investigation into the Liars and their possible connection to Wilden's death. Emily panics when her parents come under undue scrutiny due to "A's" manipulations. Hanna bristles when Caleb tries to help her through her this latest crisis, and tries to shift the focus of the police investigation. And Toby finds a new source of information into his mother's death, but it only leads to more questions. Meanwhile Aria has an uncomfortable encounter while out with Jake, and Spencer lays a trap for Melissa.

Hanna's new interest in crime novels helps her to come up with a plan to try and figure out whose body is in Ali's grave. While Hanna is on her hunt, Spencer is working overtime to decipher the stories in Ali's diary which she hopes will reveal the identity of Ali's mystery man. But with both girls hot on the trail, will their work lead them straight into "A's" path? Meanwhile, Aria is upset with the new friend Mike has made and Emily's dad is concerned about her behavior.

With Spencer’s possible Board Shorts revelation, she is now more determined than ever to prove her theory before bringing it to the other girls’ attention – especially since it could have a devastating effect on one of the Liars. But with many sleepless nights fueled by prescription medication, Hanna starts to notice Spencer’s odd behavior. Will Detective Hanna be able to figure out Spencer’s secret before Spencer is ready to share? Meanwhile, Emily looks to make amends with Alison through Shana, and all of Aria’s lies start to take a toll on her.

Emily, Hanna and Spencer are concerned for Aria as they watch their friend crumble after learning shocking news about Ezra. Not knowing what is true or what to trust, Aria goes looking for answers, not wanting to believe this revelation to be true. While concerned for Aria, Spencer is not doing so well herself. Trying to prove to her parents and Toby that she can kick the habit on her own, Spencer has to be careful because one misstep could send her to rehab. But can Spencer really rein it in, or will her constant curiosity and drive be her undoing? Meanwhile, Paige has had enough with Emily’s secrets and is determined to stop it.

Emily takes up the sleuthing reins as she searches for answers about Ezra and Mona. After confronting both, Emily tries to make sense of the heartbreaking situation. Hanna, on the other hand, begins a new search after being confronted by Det. Holbrook and Lt. Tanner with a possible new lead in Alison’s case.Meanwhile, Spencer and Aria lean on new men in their lives to recover.

It is a rough time for all of the Liars as Spencer is reeling about the memories from her lost summer, Aria is still nursing a broken heart, Emily is reeling from Paige's Betrayal and Hanna unsuccessfully attempts to wade back into the dating pool. But as each girl tries to deal with her individual issues, they must focus their attention on their suspicions surrounding Mrs. DiLaurentis. Assuming that Mrs. D knows more about Ali and the night she went missing, girls decide to help out at her charity bridal fashion show to gain access to the DiLaurentis house to search for answers. Meanwhile, Ella and Jason return to Rosewood, each with something to hide.

After years of questions and mystery surrounding the night Alison DiLaurentis disappeared, her four best friends come face to face with Ali and finally learn what really happened to her that September night. Now with their newfound knowledge of Ali’s long-held secrets, can Aria, Emily, Hanna and Spencer help Alison finally figure out who “A” is?

Aria watches over Ezra at the hospital, while Alison and the others set a trap for "A."

Emily, Spencer and Hanna try to adjust to the new normal; Kenneth searches for Jessica.

Aria, Emily, Hanna and Spencer feel trapped and search desperately for a way out of a bad situation.

The girls are not feeling merry at Christmas because Spencer's murder charge looms over them. Things improve though after they see an opportunity to gather evidence to clear her name.

Mona's friend comes to town to pay her respects.

Aria hopes Andrew can be her tutor; Spencer helps Jonny with a new project.