The circumstances surrounding Alison's disappearance continue to haunt Aria, Emily, Spencer and Hanna as questions arise about the night she went missing.

As they try to pay tribute to Alison's memory, the four friends are faced with unresolved issues. With 'A' taunting them every step of the way, can the girls forge ahead and leave the past behind?

To the girls' dismay, Mona is headed back to Rosewood High. Aria, Emily, Hanna and Spencer take very different views of the "new" Mona.