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Alison DiLaurentis goes missing from Rosewood mysteriously and the four friends Aria Montgomery, Emily Fields, Hanna Marin, and Spencer Hastings drift apart. -
Aria returns to Rosewood after spending a year in Iceland with her family, and the girls reunite. -
The girls receive mysterious texts from someone called "A" threatening to reveal their deepest secrets. -
The girls attend the homecoming dance at Rosewood High School where they receive a note from "A" warning them about Toby Cavanaugh. -
Toby is arrested for Alison's murder, and the girls believe they are safe from "A." -
Emily's girlfriend Maya St. Germain is sent away to a juvenile detention center for drug possession, which Emily's mother made sure of. -
The girls' friendship becomes strained as they struggle with their own secrets and try to uncover the identity of "A". They also begin to suspect that Alison might still be alive. -
The girls' suspicions about Alison's possible survival are confirmed when they receive a video of her alive and well, but the source of the video remains unknown.
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A new "A" emerges and begins tormenting the girls with even more dangerous and life-threatening situations. -
The girls discover that "A" is Mona Vanderwaal, a former friend who they thought had been killed in a car accident. -
Mona is sent to a mental institution, but the girls continue to receive messages from "A", leading them to believe that someone else must be helping her. A new "A" appears, who is even more ruthless and dangerous than Mona.
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Hanna's mother Ashley Marin is arrested for the murder of Detective Darren Wilden. The girls try to figure out wether Hannas mom did it or if "A" set her up. -
The girls discover that the new "A" is CeCe Drake, a former friend of Alison's who is also her long-lost sister. CeCe is revealed to be transgender, and her identity as "A" causes a rift in the group as they struggle to come to terms with her actions. -
The girls graduate from high school and begin to move on with their lives, but "A" continues to torment them. -
Alison returns to town and reveals that she has been alive and hiding for the past few years, but she also has secrets of her own. -
The girls attend college and try to leave their past behind, but they soon realize that "A" is still targeting them.
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The girls discover that Alison has a twin sister, Courtney, who was the one who went missing on the night of the sleepover, and Alison took her place to protect her.
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The identity of "A" is finally revealed to be Alison's cousin (CeCe Drake), who was seeking revenge against the girls for their involvement in Alison and Courtney's past. -
The girls finally put an end to "A's" reign of terror and bring the person to justice. The girls attend their college graduation and reflect on their experiences over the past few years.
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The girls reunite after five years and realize that "A" might not be gone for good. -
A new group of teenage girls in town receive a text from "A", hinting that the cycle of torment might start all over again.