Last week we got a small taste of the musical 'Grease'. Multiply that by 100 and you have this episode of 'Glee', which focuses on the New Directions as they perform the school musical 'Grease.' Rev your engines and put on your poodle skirts Gleeks, not since 'The Rocky Horror Glee Show' has there been an episode this big.

Mr. Schuester (Matthew Morrison) tells a very distraught glee club that he will be leaving McKinley High at the end of the week to help out the arts, but will be back after Sectionals. In order to appease them he introduces their new group leader Finn Hudson (Cory Monteith), who tries to assure them he is completely capable of leading them while Mr. S. is gone.

Enter Sue (Jane Lynch) who calls them into Principal Figgin's (Iqbal Theba's) office for a meeting. She promises that if Finn runs the club, her reign of peace with the glee club will be over. To prove her point, she terrorizes the students standing outside.

In New York, an excited Rachel (Lea Michele) is ready to focus on her career, telling new love interest Brody (Dean Greyer) that she has an audition for a new musical version of 'The Glass Menagerie.' Cassandra (Kate Hudson), overhearing the conversation warns her to be prepared and Rachel invites her along to audition for the role of her mother. In response, Cassandra asks Brody to be her T.A. to keep him away from Rachel.

Back at the school, Marley (Melissa Benoist) is having trouble fitting into her Sandy costume. Kitty (Becca Tobin) mocks her weight gain and we learn through flashbacks that she's been purposefully shrinking Marley's costumes to destroy her confidence. Kitty then invites everyone over for a sleepover. Even Unique (Wade Adams)!

Marley goes to talk to her mom about her weight gain because she's worried she will end up like her overweight mother. She tells Marley that she has to fight to stay skinny and they both agree to go on a diet together.

Finn heads to the teacher's lounge to apologize to Sue for insulting her baby in 'The Role You Were Born To Play,' but she kicks him out for not being a member of the faculty. She also informs him they will have to find a new place to rehearse as she has reserved the auditorium for the Cheerios.

The boys arrive at the Hummel tire shop for rehearsal and fix cars while they sing 'Greased Lightning' led by Ryder (Blake Jenner).

Kurt (Chris Colfer) and Rachel discuss the musical at McKinley, with Kurt thinking they should go back so he can see Blaine (Darren Criss). Cassandra overhears them and tells the pair to go, even uncharacteristically giving them her frequent flyer miles so they can travel back to Ohio.

At the aforementioned sleepover, Kitty suggests Marley should become bulimic to stay thin since she was born with the "fat gene." While she is out of the room, Kitty and the other girls mock Marley by singing, 'Look at Me, I'm Sandra Dee.'

Finn has more Sue problems when he's called into Figgin's office to talk to Unique's parents (who didn't know he was playing a female in the school play). They pull him out of the musical and say he has to dress like a boy during school hours.

To make up for the missing cast member, Finn calls in Santana (Naya Rivera), who is proud to take on the role. This doesn't sit well with Tina (Jenna Ushkowitz), who was hoping for the part.

Rachel and Kurt arrive at their old school and are greeted by Mercedes (Amber Riley), who takes them backstage. There Kurt runs into Blaine and Rachel runs into Finn, and it's awkward all around.

The play starts with Blaine performing 'Beauty School Dropout' while Kurt watches him sadly.

Meanwhile, Marley is backstage making herself throw up so she doesn't end up like her mother. Ryder finds her there and forces her to stop, reminding her hurting herself isn't worth it. She sings a reprise of 'Look at Me, I'm Sandra Dee' now that she's more at peace with herself.

Santana and Brittany (Heather Morris) talk backstage about their relationship status, with Brittany suggesting Santana should think about their breakup while singing her sad song onstage. Santana sings 'There Are Worse Things I Could Do', accompanied by Unique who is singing along from the audience, and Cassandra who is singing while performing racy dances with Brody in New York. As the song ends, Brody and Cassandra kiss.

Mike (Harry Shum Jr.) and Tina briefly discuss their own relationship problems and agree to discuss getting back together.

Marley has now changed into her finale outfit (the skin-tight black Sandy suit) and Ryder tells her she looks amazing. Kitty tries to once again destroy her confidence by saying the editor of the McKinley Muckraker is in the audience to write a scathing review of the play. Ryder tells Marley to ignore Kitty's jabs and he kisses her while Jake (Jacob Artist) sadly watches from across the room.

The play ends with Ryder, Marley and the rest of the cast performing 'You're the One That I Want.' From the audience, Rachel imagines she and Finn are up there performing it together, along with the rest of the original 'Glee' cast -- at least the ones in this episode.

Shaken up by the whole thing, Rachel calls Brody, but Cassandra answers his phone, saying Brody is in the shower. Cassandra tells a confused Rachel this is her payback for recommending she "get back in the game." A teary-eyed Rachel hangs up.

After the show, Finn finds her in the hallway crying. He thanks her for coming but is hurt that she's crying over Brody. They agree they should continue to keep their distance from one another because it's for the best.

Blaine tries to talk to Kurt about how he cheated on him. Kurt doesn't want to hear any of it because their relationship can no longer be a trustworthy one.

Inside the glee room, Artie (Kevin McHale) reads their glowing review and everyone celebrates. Mr. S. says goodbye, knowing he left them all in good hands. He thanks them for giving him happiness and allowing him to share it with others. He also expects another Sectionals trophy when he returns.

Finn walks Will out (who tries to talk shop), but Finn assures him he can take care of everything. They share a bromantic hug and Mr. Schuester leaves as Finn smiles.