Garbage collector Marty Malt debuts his stand-up comedy act at Syd’s nightclub to an unresponsive audience. Despite Marty’s poor delivery and unfunny jokes, Syd pays him to appear at the club two nights per week. Afterward, Marty’s friend, Gus, praises the performance, hoping to join the act as an accordion player. Rosarita, a waitress at the neighborhood diner, spends the night with Marty, ignoring him as he concocts new jokes in bed. At the city dump, Gus discovers the corpse of a young woman and removes a pair of earrings clutched in her hand, which he later presents to his obese girl friend, Nicolette. The following evening, Gus tells Marty about his chance encounter with talent agent Jackie Chrome, who has been convinced to attend the next performance. Concerned about a large pimple on his back, Marty consults Dr. Scurvy, who charges $250 for his opinion that the blemish will vanish over time. Marty delivers groceries to his chain-smoking mother, who suffers from emphysema. She responds to the news of her son’s burgeoning comedy career by reminding him that he is not funny. Jackie Chrome attends Marty’s performance and walks out in disgust after two jokes. Gus spares Marty’s feelings, attributing Jackie’s disdain to a lack of sophistication. When they reach Marty’s apartment, Gus discovers a tiny hand protruding from his friend’s back. The next day, Dr. Scurvy dismisses the appendage as an everyday occurrence, while Rosarita is appalled by it and ends her romance with Marty. That night, Gus brings Nicolette and two other obese women, Pickles and Shirley, to Marty’s apartment, asking to see his third hand. Marty removes his shirt, revealing a fully developed arm. The mutant limb titillates the women, and Marty is told to stay in the kitchen while Gus conducts an orgy in the living room. Marty is fired from Syd’s and replaced with Rufus Bing, an equally bad comedian with a more enthusiastic delivery style. Gus believes the third arm can revive Marty’s career, and takes him to Jackie Chrome’s office. The agent is impressed with Marty’s extra limb, and assigns Marty the name, “Desi, the Three-Armed Wonder Comic.” Gus joins the act as musical accompanist, and the team is booked into several nightclubs. Jackie also commissions a custom suit for his client, with a third sleeve in the back. Marty and Gus debut the act, in which the comedian spins slowly to display his third arm after each joke. The weak audience response inspires Gus to “add motion” by repositioning himself on either side of Marty throughout the performance. Aware that Marty is saddened by his failed romance, Gus offers to intervene, but uses the opportunity to disparage his friend and seduce Rosarita. Their next performance is interrupted by Sloppy, owner of the nightclub, who ejects the team with a warning to never return. However, Jackie convinces his clients that Sloppy loved the act, and was angry over being refused an exclusive engagement. That night, Marty dreams that Rosarita emerges from the ocean and declares her love, then screams in terror as Marty’s body is engulfed in extraneous arms. In the morning, Jackie informs his clients of their upcoming television debut on the local program, Twinkie Doodle’s Amateur Spotlight. The performance is poorly received by the studio audience, comprised of small children. Mrs,. Malt can only tolerate a few seconds of her son’s act before changing the channel, while Rosarita watches attentively at the diner. Afterward, Marty, Gus, and Jackie are greeted backstage by Dirk Delta, talent scout for The Danny Dugan Show in Hollywood, California, who hires the act for the following week’s broadcast. As Jackie and his clients leave the studio, Marty stops in front of the diner and gazes through the window at Rosarita, who sits sobbing. In the morning, Marty and Gus discover that the third arm has disappeared. Furious over this development, Gus threatens Marty with a baseball bat, then decides to fashion the bat into a prosthetic arm. The team enters Jackie’s office to confirm their booking with Dirk Delta, but when the agent asks Marty to spin several times “for good luck,” the false arm flies across the room. Although Jackie believes their chances are ruined, he agrees to call Dirk and explain the loss of Marty’s third arm. The talent scout surprises Jackie by honoring his promise, but invites only Gus to perform on the program, as Marty is no longer remarkable. The following Tuesday, Marty says goodbye to Gus and Jackie as they leave for Hollywood, certain of their imminent success. Later, Marty visits the diner to find that Rosarita no longer works there. He returns to Syd’s with a new comedy routine, and regales the audience with jokes about his third arm.