Pll season 7 overview!

7x07 Original G'A'ngsters

Synopsis: Jason returns to town to stop Ali from getting too close to Mary. The girls learn something new about Mary and Mrs. DiLaurentis that leads them to a storm cellar full of clues. Ezra gets a call about someone in his past that could change his course. Noel Kahn grows more and more suspicious and rises to the top of the list of suspects for Uber A.

Main cast:
Troian Bellisario as Spencer Hastings
Ashley Benson as Hanna Marin
Lucy Hale as Aria Montgomery
Shay Mitchell as Emily Fields
Janel Parrish as Mona Vanderwaal (credited only)
Sasha Pieterse as Alison DiLaurentis

Supporting cast:
Tyler Blackburn as Caleb Rivers
Ian Harding as Ezra Fitz
Andrea Parker as Mary Drake and Jessica DiLaurentis
Keegan Allen as Toby Cavanaugh
Drew Van Acker as Jason DiLaurentis
Nia Peeples as Pam Fields
Lulu Brud as Sabrina
Kara Royster as Yvonne Phillips
Tammin Sursok as Jenna Marshall

Featured music:
"Who Are You" by Ivan & Alyosha - (The girls celebrate Aria engagement over brunch at The Radley; Spencer gives the girls monogrammed bracelets then the girls toast to Aria's engagement; A.D. has a message delivered to the girls)
"Blood Love (Big Wild Remix)" by Young Summer - (Spencer has coffee at The Brew then decides to go over to talk with Toby, she questions him about Jenna's intention on her return which he tells her she came back for forgiveness)
"Bright Side" by Johnny Stimson - (Overwhelmed by wedding details, Ezra suggests to Aria that they elope and get married in Italy)
"She Devil" by The Knot - (Aria gets a text from Jason; Emily bartends at The Radley where she brings over a drink to Noel Kahn)
"This Never Happened" by Nevada Wild - (Aria and Jason meet up at The Brew, they promise to keep their past tryst a secret then Jason asks for Aria to help find evidence that Mary was involved with Elliott and selling Carissimi Group funds)
"Red Eyes" by Alexx Mack - (Emily greets her mother as she arrives at the bar at The Radley; Emily receives a text from Spencer which she lies to her mother about just when a bachelorette party comes in)
"Follow The Lines" by Spencer Thomson - (Emily notices her mother not enjoying herself as the bachelorette party grows louder, she questions her mood then reminds her that her father would have wanted her to enjoy life like he did)
"Paradise" by clementine & the galaxy - (Emily and Aria watches Pam as she dances; Aria tells Emily about the storm cellar and suggests that they go there but Emily convinces her go with Ezra to Italy to get married instead of hanging back)
"My Type" by SAINT MOTEL - (Pam returns to the table to tell Emily about all the plans she's made with her new friends which Emily praises her for then Emily pulls her to the dance floor to enjoy the rest of the party)

Episode storyline:
Jason DiLaurentis comes back to Rosewood in this episode. He still believes that Mary is working with Archer.
It is revealed that Aria and Jason hooked up during the five year time jump. Noel Kahn broke into Toby's airstream to steal Mary's file. Mary confesses to Jason, Alison, and Aria that Jessica had told her Charles had died under her care. She also claims Jessica spent a lot of time down in a storm cellar at their Aunt Carol's house. Toby goes to Spencer and reveals her that the house he started building in Rosewood was originally for her--not Yvonne, he also tells her he and Yvonne are going to move to Maine to start their family. The Liars minus Aria and Mona go to investigate to the storm cellar, and discover Jessica had turned it into her lair. Through photos, Alison realizes her mother must have known that she was still alive and searched for her. Jessica had also kept files on all the Liars and had all of Mary's medical history. In there, the girls discover that Mary had a second child. Their gender is undisclosed, but he/she is the same age as the Liars. Ezra gets informed by the FBI that they have reason to believe Nicole is alive. A.D. steals the files that Jessica had of Aria and Noel, drenching the latter with alcohol and lighting a match to burn it. It is presumed that A.D. could have also been responsible for the torching of the storm cellar.

Information from pretty little liars Wikipedia