On the way home, Marge and the kids smell something awful. They pinpoint the source to Maggie, who has soiled her diaper and needs a change. Marge quickly pulls into the Kwik-E-Mart, and Apu is reluctant about letting Marge use the restroom, but when he smells Maggie, he allows it. Later, as Marge comes out with a much sweeter-smelling Maggie, a shady character in a Goofy hat accosts her and threatens her with a gun. Finding only diapers in Marge's purse, he grabs Marge's pearl necklace and takes off. Marge, stunned, walks to her car in a daze and breaks down sobbing at the wheel in front of her kids.
The next day, they inform the cops and Chief Wiggum declares he will get on it right away. Later, as Marge is about to leave the house, Homer gives her some pepper spray and some tips on how to handle an attacker. She pulls up to the Kwik-E-Mart, but she is scared when Ralph greets her. She pepper-sprays him, and feeling guilty, she drives back home where it's safe. When she reaches home, Bart tells her she is parked over the mailman. Marge is a nervous wreck and cannot bring herself to cross the threshold of her house. Homer and the kids try their level best to encourage her to go outside, but to no avail. Finally, she moves into the basement. There, feeling a bit safer, she prepares breakfast for the family and sets up a bed for herself. One day, when she is alone at home, feeling bored but still afraid to venture outside, she eyes Rainier Wolfcastle's weight-lifting set and decides to use it to pass the time.
In two weeks, she builds herself up and even gets a well-defined washboard stomach (much to Homer's delight). Suddenly, she dashes out to the garden to get some lemons. Realising that she is not afraid anymore, she starts running around town in happiness. Suddenly, she runs into her mugger, who tries to assault her again. But this time, she beats him so intensely he is left a bloody mess. The cops arrive and arrest the crook. Marge, pumped after catching the crook, starts exercising even more (to the theme from Rocky). One day, as she jogs by an open-air gym at the beach, an accurate portrayal of Muscle Beach in Venice, California, she runs into Ruth Powers, her old neighbor from "New Kid on the Block" and "Marge on the Lam". Ruth, pretty buffed herself, tells Marge that she owes it all to steroids. She talks Marge into using them, attacking her inability to stop trying to be stronger, and also attacking her wish not to be weak and helpless, she also advises Marge to enter a women's bodybuilding contest. Marge, using the steroids, exercises harder than ever, and becomes vastly muscular and estrogen-depleted, resulting in extreme bad temper and belligerence. Homer, seeing these changes, starts to lose his attraction to her. When Homer refuses Marge's sexual advances the night before the contest, trying to convince her that the steroids are a bad idea, she callously ignores his worries and then proceeds to pin him down and rape him, before leaving him to take care of the kids the next morning. At the contest, despite her massive training, she wins second place, which irritates Marge when her muscular ears overhear her family's conversation in the audience.
Later that night, at Moe's, Marge tells everyone at the bar that she's going to exercise and take more steroids so she'll never come in second place again. Things get worse when Moe tells Marge that she's no longer attractive and everyone at the bar tries to attack her. Marge fights back (even taking out five sailors as they march in to get her) and ultimately trashes the bar. Homer (who has been hiding in the backroom) comes out to confront his wife as she prepares to hurl Lenny at him. Homer whimpers that he wish Marge was the sweet woman he married instead of the steroid-pumped monster she's become. Marge, horrified with what she has done, apologizes and leaves with Homer. Moe, in order to cover the costs of repairing his bar, sets fire to it; however, Carl points out that he has not insured the place yet (even though it was established in Dumbbell Indemnity that Moe did have insurance for his bar). Later, at the Simpson house, Marge burns the weight set in the furnace as the show ends. Homer asks if Marge is ready for a "real workout" which turns out to be a request to wax the car.