The Study Group returns from summer break ready to tackle their fourth year of Community College. Jeff is particularly focused on graduating and is just a few credits away. When there is a mix-up with a history class registration, Dean Pelton institutes an elaborate physical competition for class space. Meanwhile, Britta helps Abed deal with the anxiety he is experiencing over the thought of the study group graduating and breaking up.
While on their way to Vicki's Halloween costume party, the study group makes a detour to Pierce's mansion when they learn he accidentally locked himself in his panic room. As Pierce languishes behind locked doors, the group searches the dark and eerie house for the book that holds the code to the door. Along the way they encounter a few of the house's secrets.
In support of Troy and Abed, the study group heads to InspecTiCon - the annual Inspector Spacetime Convention. Trouble begins when the group meets up with Abed's email "pen-pal", Toby Davies, who's shared passion for Inspector Spacetime comes between Abed and Troy. Meanwhile, Annie leaves the convention floor to enjoy the luxuries of the hotel while Jeff relaxes in the bar with Lauren, an Inspector Spacetime fan.
After losing out in registration for "The History of Ice Cream", the study group begins their European History class with Professor Noel Cornwallis. To make matters worse, the group encounters the return of the arrogant German students from last season, which Jeff and Shirley faced over the foosball table. Meanwhile, much to Dean Pelton's dismay, Chang makes his return to campus.
The study group heads to Shirley's for a Bennett-filled thanksgiving, which is so awkward that they immediately begin plotting their escape. Meanwhile, Jeff heads to his estranged father William's house, whom he hasn't seen since he was a child.
As the campus strives to get to the bottom of Chang's memory loss, Dean Pelton enlists the group to help secure a grant for further medical research and Abed films the activities for a documentary. Jeff, however, suspects there is more to Chang's memory loss than meets the eye.
Dean Pelton sets his sights on "whale" (otherwise known as a wealthy potential student) and enlists Jeff, Britta and Annie to help in his recruiting efforts. Pierce finds out and is incensed. Meanwhile, Abed begins a new Greendale fraternity, while Troy and Shirley begin a physical education instruction class, in which Shirley excels and Troy struggles.
When Dean Pelton plans a "Sadie Hawkins" dance at Greendale, Britta plans a competing "Sophie B. Hawkins" dance in protest - but the joke is on Britta - who has confused Sophie B. Hawkins with Susan B. Anthony.
The study group takes a wild balloon ride that crash lands in the woods and they end up spending some quality time together with a friendly mountain man.
Jeff organizes a lovely holiday gathering at his apartment but Annie secretly invites Professor Cornwallis, to get in his good graces. When it becomes apparent that Professor Cornwallis intends to give them a bad grade on their joint History paper, the atmosphere quickly deteriorates and the group takes decisive action.
When Annie and Shirley learn that Leonard is actually holding the spot as the class valedictorian, they join forces to bring him down. Meanwhile, Troy and Abed reminisce about one of their favorite body switching films and when they inadvertently re-enact a critical scene, things start becoming a little funky at Greendale.
Abed, becomes convinced that the study group was destined to meet at Greendale and pieces together everyone's past - revealing that their lives have been intertwined for years. Meanwhile, Chang plots to destroy Greendale once and for all.
Jeff achieves enough credits to graduate and contemplates graduation - and beyond. Meanwhile, the study group revisits the 'darkest timeline'.