It's Green Week on NBC and to celebrate, the Dean renames Greendale to Environdale, until Star Burns is quick to point out the school was already named Green. But hey, at least the Dean booked Green Daye (not to be confused with Green Day like the Dean was).
In Spanish class, Annie takes too long to put down her pencil after a test and the whole class is punished with a paper that turns into a thirty page paper as they continue to complain. The group sends in Jeff to talk Chang out of it. Jeff figures out it's because Chang's ex-wife left him but is only able to get himself out of the paper when he begins hanging out with Chang outside of school.
When Shirley is too nervous to give her presentation on selling brownies on the Internet, Pierce, of course, volunteers to help her. He teaches her the tricks to public speaking and tells her to ditch the cards. However, when it comes time to the actual presentation she goes with the cards and her nervous old habits and gets cut off to stop by the teacher.
Abed and Troy have a biology lab where they have to teach their rat to respond to a song. They name their rat Fievel and choose "Somewhere Out There" from An American Tail. Cute. However, Troy's fear of rats ends up letting their mouse escape. Troy refuses to help Abed look for the rat, and Abed gives him a friendship speech and heads off to find Fievel himself. He sees him escape down the hall and begins singing "Somewhere Out There."
As Troy begins to sing, Jeff brings Chang to the Green Daye concert and has a surprise their... his ex-wife. He must win her back the way he original won her... with dance! As Green Daye plays, the vocals are Abed, soon joined by Troy, singing their song. We get a montage of Shirley finally listening to Pierce's advice and nailing it, Chang winning back his ex-wife, and, of course, Troy and Abed successfully recovering their rat.