Homer fakes his own death so he that he can enjoy his Saturday at home rather than help his co-workers collect litter. After friends stop by to offer their condolances, Marge realizes what Homer has done and tells him to set things straight. At the Hall of Records. he reads a clerk's computer screen and discovers that his mother is still alive. He visits the family plot and meets his long-thought-dead-mom, who has snuck in to town to pay her final respects to her son.

Mother Simpson recounts how, 25 years earlier, she tired of her dull husband Abe and joined germ warfare protestors at Springfield State College. Caught while staging a raid on a germ lab operated by Mr. Burns, she was forced to flee the family and hide underground. Now, 25 years later, she has risked her freedom by coming back to Springfield. Soon after, Mr. Burns sees her at the post office and identifies her.

While FBI agents begin an extensive manhunt for the fugitive mom, Grampa explainns to his wife why he told Homer ahe had died rather than admit the truth. The FBI determines Mother Simpson's whereabouts and storms the Simpson home. But Mother has already fled, tipped off by Chief Wiggum, who was repaying an old debt.