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.

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.