"The Lastest Gun in the West" is the twelfth episode of Season 13.
Bart and Lisa meet a washed-up celebrity of westerns from the 1950s and attempt to revive his career by getting him to appear on the The Krusty the Clown Show. But years of alcohol abuse gets in the way.
As Bart walks home from school one day, he catches a baseball that soared all the way from the stadium. Looking down, he finds a shiny new dime and an even shinier new dime underneath it. As he continues walking home, he sees a broken down ice-cream truck. The driver offers him some free ice cream. As Bart continues towards home, he happens upon a white medium-sized dog, which he assumes of befriending with. But the dog turns out to be aggressive, and soon after Bart finds himself being chased through the streets. Bart gets home safely, but the dog's rather narrow mouth allows it to reach through the mail slot and tear Bart's clothes off. The following day when Bart tries to play a prank on Lisa and her best friend for life, Janey, the dog launches another attack. Bart grows convinced the animal is out to kill him, and shows it to the rest of the family. However, the dog acts playful and friendly towards them, expelling any reason they had to believe Bart. The next morning, Bart runs inside the school bus, but the dog is waiting for him there. After being chased off the bus Bart is nearly bitten before shoving his schoolbook into the dog's mouth yelling, "Eat my short stories!" Before the dog finishes the book, Bart puts some distance between them and wanders into an old ritzy neighborhood. Bart climbs the gate of a large old house and hops over the side, separating himself from the dog. Bart concurs that he is safe, and states that he will slowly turn around to confirm that. He turns around soon finds himself face-to-face with a wolf, rattlesnake, mountain lion and other dangerous animals.
At first, Bart is terrified. But he soon realizes the animals are all stuffed…except for an ostrich, which bites him and runs off. An aging man steps forward and introduced himself as Buck McCoy, a famous movie cowboy who appeared in Westerns in Hollywood’s golden era. Buck shows Bart a move that makes the dog roll over and wag its tail. The dog then acts friendly to Bart and leaves. Buck then takes Bart for a tour of his sumptuous home. Bart is impressed with the many pioneer items on display. When the boy returns home, he tells his family about his new friend. Grampa is greatly impressed, as he remembers Buck’s films from years earlier. Later, Bart takes Milhouse to the old house, where Buck performs impressive lasso twirls. When Bart returns home, he shows Homer and Marge a cowboy hat that Buck gave him. Homer soon grows jealous of Bart’s new friend. To compensate, Homer begins wearing a cowboy hat and bolo tie with an arrowhead clasp.
Later, Buck is invited to the Simpsons' home for dinner. After the meal, Buck shows the family highlights of his acting career. Marge believes the cowboy Western is due for a comeback. Soon after, Bart shows up at school clad in cowboy garb, and a new Western craze sweeps town. Bart and Lisa lobby Krusty the Clown to put the old cowboy star on his show. At first Krusty is reluctant to do so, labeling the craze a “fad.” But he soon gives in, and Buck begins rehearsing his routine, shooting at a cutout of the clown. Krusty is greatly impressed…and reminds Buck that millions of viewers will be watching. Buck grows nervous and soon takes to his flask. When the show goes on the air, Buck is noticeably inebriated. And when he takes aim with his gun, Buck wavers back and forth between the cutout and the real Krusty. Buck pulls the trigger and hits the real Krusty in the stomach. Buck then admits to Bart that he’s an alcoholic, much to Bart and Lisa disappointment.
Homer (caring about Bart's feelings) plans to help Buck sober up. Marge and Homer show up at Buck’s mansion and pour all his whiskey down a drain. Buck is admitted to the John Ford Center for Alcoholic Cowboys, but he grows fed up and walks out. But Homer isn’t ready to give up on Buck. News of a robbery at the National Bank of Springfield is broadcast on television, the robbers are wearing riot gear and are armed to the teeth. When the police prove to be helpless, Homer picks up the phone and calls Buck for help. He drives the old cowboy to the bank and suggests he save the day by confronting the robbers. Though he’s just an actor, Buck tosses away his flask, along with a syringe and a pornographic magazine. Homer then picks up the magazine and said "There's nothing wrong with a little hey-hey". Buck swings his lassos and announces to the robbers that the fun is over. His lasso is a weapon that the robbers are unfamiliar with, as if they try to shoot it, the bullet goes straight the hole. Buck disarms Snake and the other bad guys, who are later taken to jail. Afterward, Bart tells Buck and Homer that they are both his heroes ("along with Itchy, Scratchy, Poochie and America's Firefighters"). After saying goodbye to Bart and telling him to never bother him again, Buck goes back to his house. After he goes in, Bart is chased down the street by, presumably, the same dog from earlier.