"The past will come back to haunt you" - this saying has never been 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 Byron's old mistress, Meredith (recurring guest star AMBER BORYCKI - The Big Bang Theory, Harper's Island). Emily is forced to see Toby Cavanaugh (recurring guest star KEEGAN ALLEN) in a new light. Spencer is reeling in the wake of someone with a vengeance and Hanna is desperate to have her boyfriend forget the "old" Hanna. With "A" taunting them every step of the way, can the girls forge ahead and leave the past behind? Meanwhile, Detective Wilden (recurring guest star BRYCE JOHNSON - Popular) 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?