After escaping church, the Simpsons look for a place to eat lunch. Upon seeing that all the restaurants have long lines, the family spots a catering van setting up food at a house. The family sneaks in and gorges themselves, only to find they have snuck into a wake. Homer is asked to be a pallbearer (to which he agrees thinking the woman who asked him meant a polar bear). At the cemetery, Homer struggles with the coffin and falls into an empty grave, hurting his back in the process. At the hospital Dr. Hibbert treats Homer and sets up to give him an X-ray to check out his vertebrae. While lying on his back, Homer hears the cost of the X-ray, and lets out a "D'oh!". To the surprise of everyone, Homer's “D’oh!” sounds beautiful and operatic. Dr. Hibbert concludes that when Homer lies on his back his stomach lodges underneath his diaphragm, which in turn helps propel his powerful singing voice.
Dr. Hibbert tours Homer around the hospital while singing "If Ever I Would Leave You", to help alleviate patient suffering. Mr. Burns overhears Homer's voice and hires him to star as Rodolfo in La bohème at the Springfield Opera House. Despite having to sing on his back, Homer quickly becomes an opera star. Homer's growing fame and success gains him loyal fans, and he gives advice to famous opera singer Plácido Domingo.
Homer, Marge, Lenny and Carl share their wedding anniversary dinner at a nice restaurant. Marge tells Homer she is glad he has become famous, but she misses their privacy. After Lenny and Carl leave, Homer is hounded by adoring fans. Marge gets fed up and storms out of the restaurant and Homer follows after her. On the street, Homer tries to make up with Marge, when a large group of fans spots Homer and Marge and chases after them. Homer and Marge are trapped in an alley; just before the mob reaches them, a black clad biker on a motorcycle shows up to drive Homer and Marge to safety.
Back at home, Marge and Homer are surprised to find that the mysterious rider is a woman—Julia Eldeen (Maya Rudolph). Julia, also a fan of Homer, explains she hates how all the other fans constantly mob him. She proposes they hire her to be Homer's manager, so she can take care of everything. Marge loves the idea, and goes to the kitchen to make a celebratory pie. With Marge gone, Julia reveals her true intentions: standing naked before Homer, she says he can have her anytime he wants. She threatens to tell Marge he attacked her, should he tell.
Although crazily obsessed with Homer, Julia proves to be a great fan club president and Marge is impressed with her efficiency. Her continual sexual advances force Homer to put his foot down and fire Julia, who leaves implying she will get back at Homer. At breakfast the next day, Homer pours himself a bowl of cereal and a cobra hidden inside the cereal box attempts to attack him. Luckily, he disables the cobra by repeatedly swinging it against the refrigerator. Lisa concludes Julia is trying to kill him for firing her. Springfield's finest are put on bodyguard detail for Homer.
As Homer prepares for his next performance, Marge pleads with Chief Wiggum to cancel the show, but he convinces her that Homer will be safe, explaining that the opera house is under total surveillance. Later, while Homer performs on stage, Marge and the kids remain on the lookout for Julia. Bart spots her disguised as the conductor and Marge watches in horror as Julia loads a poison dart into her conductor’s baton. Just as Julia prepares to use her baton, Marge grabs a French horn and uses it to redirect the dart back at Julia. Upon being hit by the dart Julia falls to the ground and Chief Wiggum calls on his snipers to finish her off. Every bullet misses, except for one; a second later, the giant chandelier falls from the ceiling and crashes on top of Julia. Julia is wheeled into an ambulance, vowing to return. Homer and the family head for home and Homer announces that he is retiring from the opera and explains that he can think of a much more fun thing he can do while on his back: painting. It is shown then that he painted a version of the Sistine Chapel roof on the ceiling of his living room, with him as Adam and Marge as God. A classical operatic version of "The Simpsons Theme" plays as the credits roll over a black background.