Plot

A simpleminded, sheltered country boy suddenly decides to leave his family home to experience life in the big city, where his naivete is both his best friend and his worst enemy.

Navin is an idiot. He grew up in Mississippi as the adopted son of a black family, but on his 18th birthday he feels he wants to discover the rest of the world and sets out for St. Louis. There everyone exploits his naivete, until a simple invention brings him a fortune.—Tom Zoerner <Tom.Zoerner@informatik.uni-erlangen.de>

Of all days, the guileless Mississippi boy, Navin Johnson, discovers that he's not the natural-born child of an impecunious African-American family, on his birthday. Unable to cope with the shocking revelation, Navin, driven by a melodious tune on the radio, summons up the courage to go beyond the edge of the fence, see the world, and be somebody. As a result, his first stop in St. Louis will pave the way for remarkable achievements, tardy recognition, and of course, love; however, sometimes, the gap between success and failure can be very narrow. Will Navin ever find his place in the world?—Nick Riganas

Navin R. Johnson (Steve Martin), a homeless bum, directly addresses the camera and tells his story.

Navin is the adopted white son of African American sharecroppers in Mississippi, who grows to adulthood naively unaware of his obvious adoption. The large family lived in a small shack. The family includes mother (Mabel King), father (Richard Ward), brother Taj (Dick Anthony Williams), sister Elvira (Ren Woods), Grandma Johnson (Frances E. Williams) and many more. He stands out in his family not just because of his skin color, but also because of his utter lack of rhythm when his adopted family plays spirited blues music. He is unable to dance in rhythm to the spirited folk songs played by the family, but finds that he can do so perfectly to a champagne-style song on the radio.

One night, he hears the staid and starchy Roger Wolfe Kahn Orchestra song called "Crazy Rhythm" on the radio and his feet spontaneously begin to move with the urge to dance. He sees this as a calling (and believes that this is the kind of music that inspires him to go out into the world and be somebody) and decides to hitchhike to St. Louis, from where the song was broadcast.

On the way, he stops at a motel, where a dog wakes him up by barking at his door. Navin thinks the dog is trying to warn of a fire and decides to name the dog "Lifesaver." He wakes up all the other hotel guests to rescue them, but when everyone realizes it was a false alarm, one Asian man angrily suggests he call the dog "Shithead," which Navin takes literally. Navin takes a lift from several motorists and eventually reaches St. Louis.

Navin gets a job (and a place to sleep) at a gas station owned by Mr. Harry Hartounian (Jackie Mason). Harry pays Navin $1.10 per hour. Navin makes it a habit of sending his savings back home at regular intervals. Over a period of time Harry starts to trust Navin and even leaves him in charge of the gas station when he goes out on date with his wife. A car full of thieves rolls in to buy some gas. Navin says that they have to pay by credit card as he is all alone and the owner has asked him not to expose the cash at the gas station to customers. Navin realizes that the credit card is stolen. Navin calls the cops but then attaches a thick rope to the axle of the car and the other end to the wall of a nearby church. When the thieves realize that they have been made, they try to drive away, bringing down the church wall.

He's thrilled to find that he's listed in the local phone book, as his name is "in print" for the first time. Not long after, a gun-wielding lunatic (M. Emmet Walsh) randomly flips through the phone book and picks "Johnson, Navin R." as his next victim.

As the madman watches through his rifle scope, waiting for a clear shot, Navin fixes the slippery glasses of a customer, Stan Fox (Bill Macy), by adding a handle and a nose brake. The customer, Stan Fox, is an inventor who promises to try to market the device to split the profits 50/50 with Navin, then departs.

Seizing his chance, the crazed sniper tries to kill Navin, but fails, hitting the oil cans in the station window and a soft-drink machine.

The lunatic chases Navin to a traveling carnival, where Navin hides out, eventually getting a job with SJM Fiesta Shows as a weight guesser. While employed there, Navin meets an intimidating daredevil biker named Patty Bernstein (Catlin Adams) and has a sexual relationship with her, finally realizing what his "special purpose" (his euphemism for his penis) is for.

Later, while operating a miniature railway, he meets a cosmetologist named Marie Kimble (Bernadette Peters) and arranges a date with her. Patty confronts them, but Marie knocks her out. While courting, Navin and Marie walk along the beach and sing "Tonight You Belong to Me", with Navin playing the ukulele and Marie on the cornet. Navin and Marie fall in love, but Marie reluctantly decides to leave him because of his lack of financial security. She writes a note and slips out while Navin is in the bath.

Devastated, Navin takes Shithead and travels to Los Angeles. There, the gunman who tried to kill him-now sane and working as a private investigator-tracks him down and gives him a letter from Stan requesting a meeting. His glasses invention, now called the Opti-Grab, is selling big and he's entitled to half of the profits. Stan gives him a check for $250,000 as the first installment on his share of the profits. Now extremely rich, he finds and marries Marie, and they buy an extravagant mansion. Their life becomes one of splendor and non-stop partying.

However, motion-picture director Carl Reiner (playing himself) files a class action lawsuit against Navin, claiming that the invention caused his eyes to be crossed and as a result, the death of a stunt driver in the film he was making. Nearly ten million other people have the same complaint (including the judge and prosecution) and are awarded $10 million in damages. Bankrupt, depressed, and now homeless, he abandons Marie and is soon living on the streets. He storms out into the street after yelling at and blaming Marie. Seeing how callous and superficial they've become, Marie wears her tattered dress from the beach, and regrets requiring Navin to be rich.

His story now told, he resigns himself to a life of misery and memories of Marie, but to his amazed joy, she suddenly appears, along with Navin's family, and some more good news: Having carefully invested the small sums of money he sent home throughout the film, they've become wealthy themselves. They pick him up off the street, and he and Marie move back home into the Johnsons' new house - a much larger but identical version of their old, small shack. Once again Navin dances on the porch to folk songs, this time with perfect rhythm.