After a particularly bad day at school, Bart crashes down a flight of stairs on his skateboard, into the Legitimate Business Man Social club, a mobster's hangout. The Springfield Mafia are impressed with Bart's skills, so Fat Tony, the head of the mob, hires Bart as an errand boy and a bartender.
Marge does not like the idea however, and gets Homer to check out the people Bart is working for. Homer, however, is impressed with Fat Tony. Fat Tony finds out that Principle Skinner has plans to keep Bart after school, so the mob pay him a visit. The next day Skinner is gone, and Bart is the main suspect.
During the trial, Fat Tony rats out Bart as the murderer. The only one who can save Bart is Skinner himself, who appears during the trial and tells his story of how he got trapped in the basement after a stack of newspapers fell on him - the has nothing to do with his disappearance. Bart is cleared and the Simpsons watch a TV movie about Bart's story, which is largely exaggerated.