Homer and the kids suspect the worst when Marge calls the family away from their outdoor chores to watch TV. It turns out that Marge won a coveted “Oops Patrol” t-shirt after spotting a hilarious headline in a newspaper. Soon after, Marge dons the shirt and strolls through town with Homer. People everywhere react with envy. Later Marge realizes that Homer feels left out, and encourages him to win his own shirt. Homer starts pouring over newspapers in search of the next funny headline. He comes up empty-handed… but that night, bleary-eyed and miserable, Homer discovers a message encoded in one of the headlines (a la A Beautiful Mind). It reads, “Meet Me 4th Street Overpass Midnight.” He shows the message to Marge, who agrees it’s rather strange but chalks it up to coincidence. Homer believes the mysterious message is genuine. He wakes up Bart and the pair drive to the overpass, where they encounter Homer’s mother, who’s still being pursued by the government for her activities in the 1960s. Homer, Bart, and Mother Simpson make their way to a diner, where Mother Simpson pulls out a macaroni-covered tin can which Homer had made for her when he was little. It caused Mother Simpson to grow nostalgic, and she realized she had to see her son again, if only for a few minutes. Meanwhile Marge grows concerned for Homer and Bart’s safety. She telephones the police and asks for help. Wiggum and his men spot Mother Simpson in the diner and decide to investigate, but Homer puts his mother and Bart in the car and races off. Unfortunately Homer crashes into the police station, where cops draw their weapons and place Mother Simpson under arrest.

Mother Simpson is placed on trial for sabotaging Mr. Burns’ germ warfare lab back in the 1960s. When Homer takes the stand he begs the jury to let his mother go free, as he barely knows her. The jury is so swayed by the moving words, they tell the judge it would be impossible to find Mother Simpson guilty, so the judge orders her immediate release. Mother Simpson vows to be a better mother, and she and Homer begin spending quality time together. Homer brings her to the bar, where she meets Moe and greets the barflies, some of whom she remembers from when they were children. Later Homer steals an entire room from Flanders’ house so his mother will have somewhere nice to stay. The next day Mr. Burns renames his old germ warfare lab, which is now a museum, in Mother Simpson’s honor. Mr. Burns asks Mother Simpson to sign the museum’s guest book, which she’s more than happy to do. She mentions having signed a fake name when she visited numerous state parks. Suddenly Mr. Burns pulls out a pocket tape recorder, and declares he now has evidence that Mother Simpson violated federal law by supplying false information on national park registers. Park rangers move in and place her under arrest.

Lisa convinces Homer that Mother Simpson’s arrest is an outrage and something must be done to win her release… like holding a candlelight vigil. Homer twists Lisa’s words, agreeing they should help Mother Simpson break out of jail. Mother Simpson boards a bus and is driven to a federal prison. Along the way Homer and Bart trick the bus driver into pulling off the road. Homer climbs into the driver’s seat and pulls away at a high rate of speed. A police chase ensues, and Homer vows never to leave his mother. Mother Simpson pulls out a cattle prod, zaps Homer, and pushes him out the door. She then drives the bus off a mountain road. It plunges into a lake and sinks. Later the Simpsons pay their last respects at a cemetery. One night Homer pores over some newspaper articles, telling Marge there may still be hope for his mother, as police never recovered a body. The camera then pans down to a message hidden in the type, a message Homer fails to notice. It reads, “Homer, your mother loves you.”