After lying to Alison and Jason about Charles, Kenneth comes clean about the family’s connection to the young boy. While he won’t give much detail about Charles’ past, he say’s enough to give the PLLs a clue of where to look for the missing pieces – Radley Sanitarium. With Radley now closed and the files shipped off to be shredded, the girls must act fast before all traces of Charles’ past disappear.

Meanwhile, Caleb’s protective nature starts to pinch Hanna, and Spencer seeks a remedy for her sleeping issues.

Mona returns to Rosewood in a very fragile state as she must answer to the police for faking her death. Matters only get worse when she is confronted by Lesli’s sister about Lesli’s inadvertent involvement in Mona’s plot. Hanna is determined to help Mona out, not only to reassure her she is safe from Alison but also to try and repair Mona’s friendship with Lesli. Emily tries to help Sara with her troubled home life by encouraging her to explore the possibility of emancipation. Spencer, on the other hand, finds help from someone from her past.

Meanwhile, Alison grows closer to Lorenzo as she looks for support outside of her family.

With all signs pointing to Lesli as the tormentor in the hoodie, the PLLs are on a mission to get concrete proof before bringing their findings to the police. But as the girls ramp up their investigation, "A’s" threats escalate.

Meanwhile, a friend of Emily’s makes her a surprising offer, and Spencer is pressured by her family to make an important decision.

After their latest run-in with Charles, tensions are at an all-time high with the PLLs and the town of Rosewood. Aria’s big moment of seeing her work displayed in an art gallery is in jeopardy as Ella is determined to keep her safe at home. Hanna is still uncomfortable with the unexpected scholarship money and is determined to give it back, even if that means ruining her chances at going to her school of choice. And to top it off, the one normal high-school rite of passage the girls are looking forward to is in danger as Rosewood High is considering not letting the PLLs attend prom due to security issues.

Meanwhile, the more Alison learns about her brother the harder she finds it to connect a deranged murderer to the young blonde haired boy she sees in the photos and in her memories.

It is prom time at Rosewood High School, except for Alison, Aria, Emily, Hanna and Spencer who have been banned due to "security" concerns. As the girls see this as the final humiliating blow to their high school careers, the girls' mothers try to make the best of a bad situation by offering a home prom in Spencer's barn. At first reluctant, the PLLs agree and try to make the best out of a bad situation. But one to never miss a formal, Charles has other plans in store to make this a night they will never forget.

Meanwhile, Veronica, Pam, Ashley and Ella use prom night to touch base on everything that has happened to their daughters.