It's a beautiful day at Greendale Community College, and the study group is celebrating Troy's last day on campus. Everyone takes turns telling Troy how much they'll miss him, but the goodbyes are interrupted by the Dean's morning announcements.
Dean Pelton is joined by Abed, who declares a campus-wide game of "The Floor is Lava" to celebrate Troy's last day. The winner of the lava contest will be awarded one of Abed's comic books, which is worth $50,000. The prize is enough to get everyone on campus involved in the game.
Hopping across tables and chairs, Britta encounters Professor Duncan, who attempts to eliminate her by pushing her off of a table. Luckily, Jeff arrives to rescue Britta just in time. Britta thinks that the game is a classic avoidance tactic so that Abed won't have to deal with his feelings regarding Troy's departure, but everyone else is already sold on the game. There's no turning back now.
Jeff, Annie and Britta centipede down the hallway on chairs until they encounter the Locker Boys, a motley crew of ruffians headed by Chang, who is dressed like Rufio from The Lost Boys. Just before Chang's minions attack, Troy and Abed arrive to save their friends.
Before the battle ensues, Professor Hickey arrives on a Mad Max-inspired post-apocalyptic floor buffer, which he uses to mow down the remaining Locker Boys. Troy, Abed, Jeff and Annie manage to escape, but Britta is stranded on a trashcan. Fortunately, Hickey sympathizes with Britta's abandonment, and the two team up to end the lava game once and for all.
Troy and Abed arrive at the cafeteria, where Shirley and a gang of other students have created Shirley Island, a fortress built on tables and countertops. Hickey and Britta arrive shortly after with a small army of chair walkers. Hickey threatens to destroy Shirley's fort, but she's having none of it. A battle erupts between Shirley's army and Hickey's chair walkers, but Shirley has a secret weapon. She coats the floor with liquid butter, creating havoc for the chair walkers.
Eventually, the study group eradicates Hickey's army, but not before Annie and Jeff are eliminated from the competition. Troy and Abed emerge from Shirley's fort in an inflatable hamster ball and manage to escape the cafeteria, but Hickey and Britta are in hot pursuit.
Troy and Abed realize that their inflatable ball has sprung a leak. They'll need to ditch their transport immediately. They head to the basement, where they're temporarily safe from Hickey's floor buffer. In the basement, Troy and Abed climb along storage shelves to avoid touching the ground. Then, Troy delivers crushing news to Abed: the game has to end eventually. Abed explains that he actually sees lava on the floor because he can't cope with the idea that Troy is leaving.
Hickey and Brita arrive in the basement, and Hickey knocks all the shelves over. Britta saves her friends by pushing Hickey onto the floor. Abed decides that the only way for him to overcome his fear of Troy's departure is to sacrifice himself to his own delusion, and with that he falls into the lava.
Troy thinks that he doesn't deserve to fake live, but Britta comes up with a brilliant idea: she collects a DNA sample from fake-dead Abed and clones a new Abed. After some fake cloning, Abed wakes up. Troy admits that he's terrified to embark on his trip, and Abed says he doesn't have to. If Troy also sacrifices himself to the lava floor, then his clone can take the trip for him. Troy abides.
Afterward, Troy says goodbye to his friends. Saving the best for last, Clone Troy and Clone Abed say a tearful goodbye. LeVar Burton appears on Troy's boat to help him navigate the ship around the world. Troy seems like a new, more mature person, and while he'll miss his old friends, he's about to set off on the trip of a lifetime.
To celebrate Troy's last day on campus, Abed declares a campus-wide game of "The Floor is Lava" with a coveted $50,000 prize.