Homer fakes his own death so he can enjoy his Saturday at home instead of aiding co-workers collect litter on Mr. Burns’ stretch of highway. As news of Homer’s death spreads, neighbours and well-wishers send their condolances to the family, much to Marge’s embarrassment. When the power company shuts off electricity to the Simpson home, Homer travels to the Hall of Records and corrects the error. But as Homer reads a clerk’s computer screen, he realizes the government believes his mother is still alive. Puzzled, Homer visits the family plot at a nearby cemetary. There he meets his long-thought-dead mother, who has arrived in town to pay (what she thought were) her last respects.

Mother Simpson recounts how 25 years earlier she tired of her husband Abe’s dull existance and fled to Springfield State College, where she joined forces with anti-germ warfare protestors. The protestors staged a raid on a local germ warfare lab, operated by Montgomery Burns, and destroyed the deadly diseases. In the process, a young Chief Wiggum, who was then in charge of campus security, inhaled the anti-viral drugs and was cured of his asthema. But during the raid, Mr. Burns got a good look at Mother Simpson’s face, forcing her to flee the family and hide underground. Later, Mr. Burns notices Mother Simpson at the post office and remembers her face from the raid years earlier.

F.B.I. agents interview Mr. Burns and begin an extensive manhunt for the fugitive. Meanwhile, Grampa confronts his wife and explains why he told his son his mother died rather than admit she was a wanted criminal. The F.B.I., guided by tips from witnesses, pinpoint Mother Simpson’s whereabouts. They storm the Simpson home, but their quarry is nowhere to be found. On an isolated stretch of highway, the Simpsons bid fond farewell to Mother Simpson, who was tipped off about the raid by an ever-grateful Chief Wiggum.