The economy of Springfield is in decline, so Mayor Quimby listens to suggestions from citizens on how to improve it. Principal Skinner states that legalized gambling has helped rejuvenate run-down economies, and that it can work for Springfield as well. Everybody, even Marge, likes the idea. Mr. Burns and Mayor Quimby work together to build a casino, where Homer gets a job as a blackjack dealer. The casino is designed by Mr. Burns himself, as the proposals he received were not to his liking. While Marge waits for Homer's shift to end at the casino, she finds a quarter on the floor and uses it to play a slot machine. She wins and almost immediately becomes addicted to gambling. Meanwhile, since Bart is too young to gamble at Burns' Casino, he starts his own casino for his friends to play in his treehouse, and intercepts Robert Goulet to perform there. Burns also grows even richer, but in the process becomes a Howard Hughes-type hermit, developing a profound fear of microscopic germs, urinates in jars, and wears tissue boxes instead of shoes.
Due to her addiction, Marge spends every waking moment at the casino and neglects her family. For instance, she forgets to help Lisa make a costume for her geography pageant. Enraged, Homer bursts into the casino and barges around searching for Marge. The security cameras capture Homer's rampage, and when Burns sees him he demotes him back to his old job at the power plant. After realizing how much he misses the plant, Burns decides to return. Homer confronts Marge with her behavior, and she finally realizes that she has a problem. Lisa does win a special prize in the geography pageant, as Homer's poor costume design gives Lisa the appearance that she did the work all by herself. Ralph Wiggum receives the same prize, as his costume is simply a note taped to his shirt that reads "Idaho".