Pretty Little Liars is the story of four teen girls—Aria, Hanna, Spencer, and Emily— whose world is turned upside down when their ringleader Alison goes missing. The book begins a year after Alison’s disappearance. Aria has been abroad for a year with her family, and the other three girls have drifted apart. When Aria returns from Iceland, Alison’s body is finally found, and the four girls start receiving creepy and threatening text messages from an untraceable number.
The texts are signed “A.
A’s texts indicate she knows everything about the girls, which is dangerous because each of the girls has a secret she doesn’t want to expose. The liars also have a collective secret: They were involved in an accident that left one of their peers blind. Jenna, the blind girl, comes back for Alison’s funeral. Jenna doesn’t know that Alison was the one who set off the stink bomb that caused an explosion and blinded her.
The liars feel guilty for not talking Alison out of the dangerous prank. Alison blackmailed Jenna’s step-brother Toby, and he was forced to take the blame for the explosion.
He too returns to Rosewood after a year of being away. When it’s discovered that Alison was wearing Toby’s sweater when she died, Toby is arrested for murder. Through all of this, the mysterious A meddles with the girls’ lives: Photos of Emily’s same-sex kiss are sent to Emily’s mother, and Aria’s mom gets a letter detailing her husband’s infidelities, which Aria knew about. Via text, “A” taunts the girls to find out his/her identity during a birthday party in the woods for Mona, Hanna’s social-climbing best friend. Hanna succeeds at discovering A’s identity, but gets hit by a car before she can reveal it to anyone.