On
Kent Brockman's Channel Six "Oops Patrol" segment, he displays a humorous headline ("Mayor Unveils Erection to Cheering Crowd"), noticed and submitted by
Marge, for which she receives a free
T-shirt and other perks from the town. An envious
Homer, after trying on and stretching out Marge's shirt, attempts to find his own funny headline so he too can win a T-shirt. Homer spends the following night with newspapers plastered over his bedroom wall, exhausting himself in his search. He finds an article entitled "World's Biggest Pizza". The first letters of each line spell out an invitation for Homer to meet someone at Fourth Street Overpass at midnight. He wakes
Bart so they can both go. When they reach the overpass, the mystery person reveals herself to be
Mona Simpson, Homer's mother. At the Overpass Diner, Mona explains that the government is still hunting her because of her crime of sabotaging
Mr. Burns' germ warfare lab. Her nostalgia aroused by a macaroni pencil case Homer had made for her when he was five, her liberal links at the Springfield Shopper published the story of the giant pizza to lure Homer.
Chief Wiggum,
Lou, and
Eddie arrive at the diner, and Lou recognizes Mona. Waitress Hora lets Homer, Mona, and Bart escape through the back after they increase her tip. After they drive off, Homer rams into the police station, where Mona is arrested. At the trial, during which it is implied by Homer afterwards that Mona's ex-husband Grampa testifies against her, Homer is put on the stand and, after a long clueless pause, gives a heartfelt request that they do not take his mother away from him again. The jury, deeply moved, acquit Mona, much to Burns' fury. Mona catches up on Homer's missed childhood; giving Homer a bath, watching Homer in the school play, knitting for Homer, teaching Homer how to ride a bike, and seeing a reenactment of the birth of Bart. To make Mona more welcome, Homer steals a whole room from
Ned Flanders's house so she can have her own private bedroom. Burns renames his Germ Warfare Laboratory the "Grandma Simpson Peace Museum and Kid-teractive Learnatorium" to a crowd of cheering onlookers. Burns asks Mona to be the first to sign the museum's guest book. However, it is revealed to be a confessional trap when after signing the document, Mona says to Burns that she signed under false names while at national parks, which is a federal offense. Federal agents jump out and arrest her.
Lisa tells Homer she disagrees with what the government did with Mona, and unintentionally gives Homer the idea to break Mona out of prison. The next day, Homer and Bart trick the bus which is transferring female convicts to prison into pulling over by changing a
sign overhead to display a warning of a snowstorm ahead. As the drivers get off to put chains on the tires, Homer steals the bus and liberates the convicts as the police give chase. Not wanting Homer to be imprisoned and leave his children like she did, Mona
tases him and pushes him out of the bus onto an abandoned bed. Homer watches as the bus flies off a cliff into a lake, where it explodes and is covered by a
rockslide. The Simpsons hold a funeral for Mona and pay their respects, but the coffin (filled with last week's garbage) suddenly slides away and into a forest. Later at night, Homer pores over newspaper headlines and finds an article in which the first letter of each row spells out "IMOK" over the front and back side of the page. Taking this to be another message from his mother that she is still alive, he goes to sleep. However, he overlooks an article about a giant
taco, in which Mona encoded a long message that explains she escaped from the bus before it crashed and hitched a ride out of town. ==Cultural references==