"The Last Traction Hero" is the ninth episode of Season 28.
An accident places Homer in a cast, and in a position to sue Mr. Burns. This leaves Marge unfulfilled, so she turns to an unexpected source for romance. Meanwhile, Lisa is proclaimed "Bus Monitor" and tries to keep the peace.
Homer couldn't locate a parking space at the Nuclear Power Plant, so he plans to park in Mr. Burns' space, as he is on a hunting trip with some friends. Homer then realizes that with Burns out, he can live the wealthy life, so Homer goes around the plant using some of Burns' gadgets and wearing his clothes. However, as he was playing golf in Burns' office, Burns enters the room.
Homer gets scared and hits the ball, which bounces around until it presses the trapdoor button, making Homer fall into it. However, the pit was under renovation, so it wasn't safe for use yet. Homer hits many objects and construction materials on his way down and eventually lands on a cement mixer that is filled with concrete. The accident leaves Homer in a cast. However, he soon gets bored as he can't move his arms to do any activities.
Meanwhile, on the school bus, Dolph tries to fight Milhouse, but he accidentally hits Nelson. Shortly afterwards, the other bullies start fighting as well. With Otto unable to help, Lisa records the tussle on her cellphone and shows the video to Principal Skinner, who sees that Lisa could solve some of the bus problems, and he promotes her to school bus monitor.
In the meantime, at the power plant, Burns finds out that his trapdoor is now illegal as it has to meet with some modern standards, making Homer able to sue the plant. Fearing this, Burns sends Smithers to see Homer and convince him not to do so. However, his visit has the exact opposite effect, as Smithers reminds Homer to sue Burns.
Smithers becomes friends with Marge when they start talking about sewing patterns, but end up talking about their love for Homer/Mr. Burns. Marge starts thinking about kissing Smithers, but Burns calls him. She then goes back to Homer and they have sex. Homer is overjoyed to learn that Marge is getting her emotional needs met by her friendship with Smithers. At Burns' office, Burns gets outraged as Smithers couldn't get Homer's signature.
On the school bus, Lisa manages to organize the way the kids sit, which makes them silent. Later, she tries to make other sitting plans, such as for the cafeteria and for the playground. However, the kids are not grateful with Lisa's plans and they rebel against it. When the bus arrives at school, it is completely vandalized and on fire. The kids get off laughing while Lisa is confused as why her plan didn't work. Milhouse explains that the bus is supposed to be crazy, which makes her a bit happier.
Mr. Burns realizes that Smithers is not going to prevent Homer from suing, and decides to send him to work at the power plant location in Chernobyl as punishment. After seeing how upset Marge is about her friend leaving, Homer realizes that the only way to impede this is if he gives up on the lawsuit, which makes his lawyer crestfallen. To make his lawyer feel better, Homer chooses to create a separate lawsuit by falling down the courthouse steps, but Marge tries to save him and falls as well. They are run over by a truck and have to wear body casts, which brings them a lot closer together.
The episode finishes with Lisa in Miss Hoover's classroom, trying not to be a smarty-pants, but she couldn't handle it and gives all the correct answers, including the day of Hoover's dental appointment, much to the annoyance of her classmates.