The saying "The past will come back to haunt you" is never more true than for Aria, Spencer, Hanna and Emily. As the girls try to pay tribute to Alison's memory, the four friends are faced with unresolved issues. Aria has an unsettling encounter with her father's former mistress, Meredith. Emily is forced to see Toby Cavanaugh in a new light. Spencer is reeling in the wake of a vengeful Melissa. And Hanna is desperate to have her boyfriend, Sean, forget the "old" Hanna. With "A" taunting them every step of the way, how can the girls forge ahead and leave the past behind? Meanwhile, Detective Wilden uses his new connection to Hanna and Ashley to his benefit. But will he get the answers he's looking for by making himself at home in the Marin household?