In the aftermath of the mysterious lodge fire, Aria, Emily, Hanna, and Spencer turn to a surprising new ally to help them discover what happened that night, and to figure out Red Coat's next move. The girls are drawn into yet another murder investigation, one that puts a cloud of suspicion around them and their closest friends and family. With Red Coat lurking in the shadows and the truth about Alison closer than ever, finishing high school has never been more dangerous!