Homer test drives a new electric car so he can get a free gift. After destroying the car by driving into an ocean due to Homer thinking its the same as an amphibious vehicle, the family returns to the dealer to receive the gift, which Homer forgets to open until he is in bed with Marge. It turns out to be free tickets to a preview screening of a new Mel Gibson film, a remake of Mr. Smith Goes to Washington, which makes Homer jealous as Marge expresses an attraction to Gibson. The audience members are given comment cards to fill and the filmmakers can change the film based on their reactions. The film is enjoyed by everyone but Homer, who only likes comedy or action movies. During the screening, Gibson, having come to the test screening unannounced due to being worried that the audience wont like him playing a dramatic role, is assured by the producers that the film is wonderful. When Gibson flirts with Marge after the showing, Homer writes a negative review of the film. While reading the mostly positive comment cards after the movie, Gibson is certain that everyone loves him too much to tell him how to improve the film, but when he reads Homer's comments, he is convinced that Homer was the only person brave enough to tell him the truth.
Gibson shows up at the Simpsons' door and invites Homer and his family to come with him to Hollywood to change the film, while Homer thinks that he is out to take Marge from him. Homer and Gibson begin work on the film while the rest of the family explores Hollywood, where they encounter celebrities such as Ellen Degeneres, Eddie, the dog from Frasier, and also spot Robert Downey Jr in a shoot-out with police. When Homer's ideas prove to be stupid and pointless, including giving a random dog a close-up of its eyes shifting back and forth to show that he is evil, Gibson begins to wonder whether he made a mistake. However, he is enthusiastic when Homer tells him his ideas for the famous "filibuster" scene at the end. The next day, they present the new ending to the producers. In the new version, Mr. Smith goes berserk and slaughters every member of the United States Congress and the President in a mindless action movie sequence. The producers are horrified at this, saying that the film was meant to be the studio's prestige picture. They attempt to burn the film reel, but Homer and Gibson, determined to save their film, run away with it.
They meet up with the rest of the family at Hollywood memorabilia museum. They steal a replica of the main villain's car from The Road Warrior and engage in a ludicrous car chase through the streets of Hollywood, with the film executives on their trail. They attempt to distract the producers by throwing the Mel Gibson mannequin that was occupying the car at the producers, with Mel switching to his old Mad Max costume in the process, but this only works temporarily. Homer, taking an idea he believes to be from Braveheart, moons the executives along with Gibson so that they will stop their car out of disgust, but this fails and Homer's buttocks is caught in the car's hood. Homer and Gibson then attend the film's premiere back in Springfield, but the entire audience walks out disgusted by the new ending, and the two men are even threatened with legal action from Jimmy Stewart's granddaughter. Homer then tries to apologize to Gibson, but he does not blame him, arriving to the conclusion there is no place for violence-lovers like them in Hollywood; however, as soon as Homer suggests more nonsensical film ideas, Gibson kicks him out of his limousine and he lies on the ground shouting towards him that he fell out. The episode ends with a random dog given a close up of his eyes shifting back and forth.