When the retirement home closes, Marge invites Grampa and two other elderly folks to stay at the Simpsons' house. Nelson becomes Bart's friend, after Bart defends him for wearing used underwear, they go to a bully meet Bart is framed for shooting the leader of the bullies, Bart, Nelson and their group of bullies get in serious trouble!
Marge and Homer have a make-out session as they arrive home from their date. As the couple pays off the babysitter and ignores the overdue bills and phone calls, Lisa's hollering about Grandpa getting kicked out of the elderly home finally puts a damper on the couple's romantic night. At the retirement home, we find out that the place is in violation of several codes, for instance with the soda machine dispensing rats and the mannequin nurses coming out of the home. Grandpa Simpson has to go home with the family unless until the retirement home is cleaned. However, when Grandpa's two pals from the home are left without anyone picking them up, Marge takes them in despite Homer's difference of opinion and the Simpson's let the elderly people stay in the basement of the house.
At school, Bart and his classmates undress for gym class, Nelson reluctantly changes, but his fellow school students laugh at him when they find out he is wearing women's underwear. The laughter does not cease until Bart also discloses he wears his father's hand-me-downs from gorillas. After the class applauds Bart for defending Nelson, Nelson and Bart become close friends. With Grandpa and his friends almost dying with every activity, Homer almost dies when he sees the electric bill before Marge revives him. The negligence going around in treating Grandpa prompts Lisa to urge Homer to be nicer to Grandpa because that will be how his kids treat him when he gets old. Homer, nevertheless, makes a point to say that you don't see him acknowledging the existence of his own grandfather.
Meanwhile, Bart receives a message wrapped around a rock thrown at his bedroom window. When he slides down the drain pipe to meet the rock thrower, he is kidnapped into the night, even with Chief Wiggum and Lou watching them. When Nelson and the other bullies make their identities known to Bart, they name him honorary bully and give him a necklace of retainers. While Bart does not seem too keen on becoming a bully, Homer feels the opposite when Grandpa and his buddies induct Homer into the "club" after Homer gets an early breakfast with them. Following a trip to the mall for exercise, Grandpa pulls Homer's pants up to make them high-waisted. During a game of Bingo, an elderly hits on Homer in front of Grandpa, who warns his Homer to stay away from those women who just want a chicken dinner out of him.
Homer is in bed with Marge with a chicken meal and turns up the thermostat in the room because he's too cold. Marge also notices that Homer's wearing sock garters. Meanwhile, Bart and the bullies prepare for the Bully Summit held at Krustyland. Chester, the leader of all bullies, has called for the meeting. At the amusement park, all bullies are required to turn in their weapons, but Bart gets sidetracked and forgets to turn in his slingshot. When an elder, more rebellious bully gets a hold of Bart's slingshot during Chester's speech, the shot is on Bart, considering he's the only one in possession of the slingshot.
A hunt begins to track down Bart as they all think he did it. So Bart, Dolph, Nelson, Kearney, and Jimbo hide in one of the Ferris Wheel and try to wait it out. The Bully that shot Chester is on. They jump off and run. After the S.A.T. Preppers fail to stop them, Bart and the Bullies are running for their lives now down the street as they are being chased by all the other bully groups in a giant torn up bus. They finally make it back to the subway, but the Baseball Furries are there waiting. Bart uses his slingshot to break the street light and distract them. One stayed behind. Nelson gets talked by a baseball mascot and dies and his last words were"save our selfs." The boys make it back to Springfield just as the sun is rising. Bart and the Bullies aren’t the only ones on the beach though. Homer and the old guys just so happen to be taking a stroll too. Homer sees his son in trouble. They have to help them, except the old guys don’t really want to and start making excuses. He rushes over and punches the New Bully in the face. The New Bully proclaims he’s never been in a fight. He whines and runs off, and Homer and the gang all head home.