The school production of "Grease" is underway, and Marley (Melissa Benoist), Jake (Jacob Artist), Kitty (Becca Tobin) and football player Ryder ("Glee Project" winner Blake Jenner) compete to play "Danny" and "Sandy." Meanwhile, former Glee clubbers Mercedes (Amber Riley) and Mike (Harry Shum Jr.) return to cast the play, and Mr. Schuester (Matthew Morrison) struggles with a difficult decision.