In Los Angeles, drunk and derelict Navin Johnson addresses the audience and insists, “I am not a bum, I’m a jerk.” He begins his story by saying that he was born in Mississippi, “a poor black child”: Navin grows up in a loving family, all of whom are black. Incongruously Caucasian, Navin has trouble clapping to the beat of the blues being played on the porch. He confides to his mother that he never feels he belongs and she reveals that he is not her natural-born child, but was found on the doorstep. Overwhelmed by this information, Navin lies awake in the twilight hours, listening to the radio. When he discovers that his feet are tapping spontaneously to the music of a swing band, Navin is inspired to hitchhike to St. Louis, where the broadcast originated, to discover more about the world. At a stopover in a motel, a barking dog awakens Navin, who presumes the dog is alerting him to a fire. Pronouncing the dog a “life saver,” the panicked Navin wakes all of the motel guests. After learning that there is no fire, an annoyed guest suggests naming the dog not “Life Saver,” but “Shithead.” Arriving in St. Louis accompanied by Shithead, Navin stops at a service station restroom, where the owner, Harry Hartounian, offers Navin a maintenance job. Navin accepts and begins to send a portion of his modest wage to his family. Hartounian values Navin, and provides him free shelter in the utility closet. When Navin is left alone in charge of the station in Hartounian’s absence, three thugs attempt to pay with a credit card. By checking a list of reported credit card numbers, Navin learns the card was stolen and alerts the police. He tries to detain the thugs by tying the car to a neighboring church, but when they drive away, they drag part of the church down the street with them. Later, a new phone book is delivered to the station and Navin, who is excited to see his name printed in it, gushes that things will begin to happen to him. True to Navin’s prediction, a gun-wielding psychotic picks his name randomly from the phone book and decides to kill him. The would-be killer positions himself near the station and takes aim at Navin. Meanwhile, a motorist, Stan Fox, arrives for a fill-up. When Fox expresses frustration about his glasses slipping off his face, Navin offers to fix them by soldering an extra bar of metal that grips the nose to the frame. Impressed, Fox promises to split the profits with Navin if he can develop and market this invention. As Fox drives away, the sniper fires several shots at Navin. Although Navin is unharmed, he feels compelled to flee and hides in a carnival truck that travels to Los Angeles. Content with his new surroundings, Navin takes a job with the carnival as a weight-guesser and befriends Patty, a tough stunt motorcycle driver. Patty seduces the naïve Navin by offering to show him his “special purpose.” Their relationship continues, as Navin begins work as “Engineer Fred” for the children’s train. When Billy, a mischievous boy, attempts to drive the train away, Navin chases him and returns him to his babysitter, Marie. In gratitude, she kisses Navin and agrees to date him. Later, when Patty discovers Navin and Marie together, she is furious and threatens Marie, who knocks her out with a quick punch that wins Navin’s heart. Later, on the beach, Marie tells Navin that she needs a man with a “special purpose” in life. He explains that he does have a special purpose and makes love to her. The next morning, Navin wants to marry Marie, but she leaves before he can propose. Although depressed, Navin is determined to find Marie. He settles into an apartment, where the sniper appears on his doorstep. The man states that he had been “mixed up” because of personal troubles, but is now a private detective. He presents Navin with a letter from Stan Fox, who has made a fortune on Navin’s invention, which he calls the “Opti-Grab.” When Navin and Stan later meet, Stan gives Navin a check for $250,000, his share of the Opti-Grab earnings. After reading about Navin’s new fortune in the local paper, Marie’s mother phones Navin and directs him to her daughter’s workplace, the cosmetics department of a department store. Navin finds her and the two are soon married. After hiring a butler and housekeeper, Navin and Marie move into a giant mansion with garish décor, where they adjust to a more affluent lifestyle. Navin is approached by scheming businessmen, who invite him to invest in their housing project, but when Navin realizes they are racist bigots, he tells them he is a “nigger,” and fights them using Asian martial arts maneuvers. At an expensive restaurant, the naïve Navin asks for “fresh” wine, then is offended when served escargot, which he mistakenly thinks is an indicator of unsanitary conditions in the restaurant. To celebrate what he believes is their newfound sophistication, Navin throws a disco party. During the party, Navin and the guests watch a television news piece reporting on the success of Opti-Grab. However, the segment is interrupted by a breaking news story that director Carl Reiner is leading a class action lawsuit for negligence, because the Opti-Grab causes people to cross their eyes to the point of injury. After a cross-eyed judge and jury decide against Navin, he is forced to return his fortune to his customers. Depressed, Navin leaves Marie. Returning to the present moment, Navin concludes his story about how he came to live on the streets. Unexpectedly, Marie and Navin’s family drive up and explain how they have invested Navin’s weekly contributions from his earnings in farm land. Navin, accompanied by Marie and Shithead, return to Mississippi, where the family builds another house, which is an exact replica of the rundown family home--only larger.