In the fourth-season opener, the girls team up with Mona to try to understand "A" better. Meanwhile, Aria doesn't look forward to seeing Ezra after their breakup; Emily makes plans for her future; and "A" charts a new course for Toby.
"A" almost kills Mona. Meanwhile, Aria takes self-defense lessons; Alison's mom gives Hanna a parrot; Toby reveals a poignant secret to Spencer; and Hanna uncovers something surprising about her mother.
The girls are curious about Melissa's return visit to Rosewood. Meanwhile, Hanna meets with Det. Holbrook in an attempt to help her mom; a clue left by Ali leads the girls to an eerie mask maker; and Emily's mother is targeted by "A."
A new detective arrives in town and questions the girls about Wilden's death. Meanwhile, Emily worries about the problems "A" is causing for her parents; Hanna is reluctant to accept Caleb's help; and Spencer sets a trap for her sister.
Spencer and Emily tour a college for different reasons: Spencer digs into Ali's link to the school, while Emily ponders her academic future. Elsewhere, Aria and her brother have a disagreement regarding their parents; Hanna uncovers something disturbing among her mom's things.
Hanna lands in trouble while trying to protect her mom. Meanwhile, Emily attempts to assist Hanna, but this displeases "A"; Spencer and Toby head to Ravenswood, which turns out to be a very unusual town; and Shana shows up in some unexpected places.
Caleb and Toby work together to investigate "A" and the incident involving the lodge fire. Meanwhile, Hanna tries to pretend that she's fine, but her pals worry about her; Aria finds Mike's behavior troubling; and Ezra's unsure of his role in Ari's life.
Hanna joins forces with Mona to help Ashley, despite Caleb's objections. Elsewhere, Spencer looks into Wilden's connection to another death; Emily reconnects with Zoe; and Jake helps Aria gain insight into her brother's new attitude.
Paige throws Emily a surprise birthday party with unexpected guests: Jenna and Shana. Meanwhile, Mona helps out Hanna and Ashley; Ezra receives some upsetting news; and Emily meets with a prestigious swimming coach.
Mrs. DiLaurentis asks Emily to move into Alison's old room. Meanwhile, Ashley's good luck changes; Ezra gets more bad news about his son; Aria tries to take an interest in Jake's hobbies; and "A" toys with a vulnerable Toby.
The girls try to corner "A" at their school's hoedown. Meanwhile, Hanna is stalked by a classmate who has an explosive secret; Ezra seeks help from Aria just as she decides to commit to Jake; and "A" continues to manipulate Toby by promising to reveal info about his mom's death.
After receiving an intriguing riddle from "A," the girls embark on a road trip to Ravenswood, where they are surrounded by familiar faces. Later, one of the foursome disappears during a magic show; and a shocking discovery could mean war. Elsewhere, Hanna's joy over reuniting with her mother is cut short; and Toby uncovers something surprising about Wren.
The girls don Edwardian wear and head to a cemetery party to see if Ali is still alive, because a clue left by "A" suggests that she might be. Meanwhile, Caleb travels to Ravenswood and encounters a kindred spirit on his journey.
The girls try to figure out who's buried in Alison's grave. Meanwhile, Caleb visits Rosewood; Ezra arranges some secret meetings; and Emily struggles to come to terms with the revelation that Alison is alive.
The girls read Ali's diary and attempt to crack its code, but this proves difficult, especially because it's full of deeply personal stories about all of them. Meanwhile, communication between Spencer's dad and Ali's mom arouses suspicion in Spencer.
Shana returns to town with a message from Ali, as well as an invitation for Emily to meet with Ali, but the girls question Shana's trustworthiness. Meanwhile, matters of the heart affect Aria and Hanna.
Aria's brother befriends Mona, but Aria disapproves. Elsewhere, Spencer digs into a new lead from Ali's diary and uncovers something shocking; Hanna's love of crime novels leads her to investigate Ali's grave; and Emily's dad grows worried about her.
Spencer struggles to sleep and Hanna worries about her as her behavior gets eccentric. Elsewhere, Emily tries to mend fences with Alison; and Aria's many fibs begin to weigh on her.
A frazzled Spencer envisions her life as a 1940s film noir as she searches for Ali and tries to find answers to her many questions.
Spencer wants to share her doubts about Ezra with Aria, but Ezra brings up her addiction problem first, undermining her credibility with her friends.
Aria begins to fall apart after learning of Ezra's betrayal, and she doesn't know whom to trust. Meanwhile, Spencer tries to show Toby and her family that she can fight her addiction without going to rehab; and Paige gets fed up with Emily's secrets.
Emily confronts Ezra and Mona as she looks for answers. Elsewhere, Hanna tracks a new lead in Alison's case after she speaks with the police; and Spencer and Aria turn to new men as they try to pick up the pieces of their lives.
The girls take part in a bridal fashion show for charity in order to get closer to Ali's mom, who they suspect may be hiding some secrets. Meanwhile, Ella and Jason return to town; Aria continues to cope with her heartbreak; and Hanna tries dating again.
In the fourth-season finale, the girls get answers about Ali and the night she vanished after they come face-to-face with her.