Crushed (2013)

"It's springtime in Rosewood, but while everyone else is searching for the perfect prom dress, Hanna, Spencer, Emily, and Aria are on a different kind of hunt: They're looking for A...Hanna puts her campaign for prom queen on the back burner to volunteer at a burn clinic, where one of A's victims is recovering. Emily digs into Ali's past at the mental hospital with some very crazy consequences. Spencer contacts an amateur private eye to help her stalk her stalker. But when their sessions get a little too private, they may forget to keep their eyes on A. And Aria's worried that A is even closer than she thought. When her dark secret from Iceland comes to light, she discovers that maybe, just maybe, the one person she's been trying to hide the truth from has known all along. The liars are finally taking the fight to A. But no matter what they do, A's always one step ahead, ready to crush the girls completely."--Dust jacket. Aria, Emily, Hanna, and Spencer prepare for prom while trying to track down A. The plot contains profanity, sexual situations, and violence. Book #13