At a diner in Denver, Dean makes a crack about Sal's age (he is a few years older than Dean), and Sal gets angry at Dean. Dean gets so upset that he goes outside to cry. Sal, feeling awful over the incident, apologizes. The two share a sad moment in the diner. Sal realizes again that he does not know who he is anymore.
Sal and Dean stay with Sal's former neighbors, a group of Okies (poor white people displaced from Oklahoma during the Depression). Dean gets in a fight with the Okie mother trying to help her buy a car. She is too indecisive for him and reminds him of his father's behavior. Dean begins looking for his father but does not find him, only finding rumors that he is working in a train yard in New England. Dean's cousin, Sam Brady, is coming into town, and Dean has to prepare Sal for his arrival. Sam was a bootlegger from Missouri who was one of the only members of Dean's family who showed him affection and care. Sal wants to know what kind of scam Dean is going to pull on his cousin, but Dean replies that there is no scam. He just wants to catch up with his cousin and remember moments from his childhood.
Dean's cousin arrives and tells him that he does not drink anymore and has found religion. He drives Dean and Sal around Denver but tells Dean the only reason he is seeing him is that he wants him to sign a paper that cuts Dean and his father out of the family will. Dean is disheartened by this news, but he continues to get excited by the stories his cousin tells him about the past. When Sam drops the two off, Sal tells Dean he is sorry that nobody believes in him-but that he will always believe in him. The two go to a carnival, where Dean thinks he is falling in love with a three-foot woman but cannot get up the courage to talk to her. When they return to the Okies' house, Dean lusts after the Okie mother's thirteen-year-old daughter.
The next day the two go to downtown Denver, where Dean steals a softball. They return to the Okies' house and start getting drunk on bourbon. Dean tries to "make it" with one of the neighbors but scares her by throwing pebbles at her windows. She starts to come after the two with a shotgun, but Sal diffuses the situation. Dean, Sal, and the Okie family then leave to get drunk at a bar. At the bar, things get frantic when Dean steals a car, goes to downtown Denver, steals another car, and then comes back. The cops show up and start investigating. Dean starts stealing more cars and eventually leaves one in the front yard of the Okie family before he passes out. Sal has to wake Dean, and they dump the stolen car so that no one will know Dean stole it.
In the morning Dean realizes the car he stole had belonged to a police detective and that the Denver police have records of his fingerprints from previous arrests. Sal and Dean decide they need to get out of town fast, so they pack their bags and say goodbye to the Okie family, a group whom Sal has come to regard as "our sweet little family." They call a cab, and after a brief scare in which Sal thinks the cab is a police cruiser, they get to Denver and catch a ride at the travel bureau.
At the travel bureau, Sal and Dean take an offer to drive a man's '47 Cadillac limousine to Chicago for him. Dean immediately begins making plans for the car in Denver (picking up women with it), but Sal is unsure. After picking up one woman and having quick sex with her, Dean picks up Sal and two boys from an Eastern Jesuit school for the road to Chicago. Two miles outside of Denver, Dean breaks the speedometer because he is driving over 110 miles per hour. Dean decides to visit his friend Ed Wall on his ranch in Colorado, but he runs the limo off a dirt road and into a ditch. A farmer helps them get the car out of the ditch, and they drive to Ed Wall's ranch while Dean tells stories of his days as a ranch hand. At Wall's ranch they eat and try to convince him that Sal owns the Cadillac and is a rich man. Wall does not believe it and thinks Dean stole the car. Like Dean's cousin, Ed Wall also has lost faith in Dean and is more concerned about his livestock than the adventures the two are having.
That night the travelers speed through Nebraska at 110 miles per hour. Dean tells Sal about a road that goes all the way through Mexico and to South America. They dream about arriving in Chicago. Dean relates stories of his past travels, getting arrested, escaping, and meeting Marylou in Los Angeles when she was fifteen. In Iowa, they get into a race with a Buick and have fantasies that they are Chicago gangsters coming into town from a trip to LA. Dean is driving recklessly through Iowa, and Sal cannot stand it anymore. He climbs into the back seat so he does not have to watch. In Des Moines, Dean gets into a fender bender but thinks he has things straightened out with the other driver. On the other side of Des Moines, however, they get pulled over and detained because the driver complained he had been in a hit and run. The mess is straightened out after a call to the Cadillac's owner.
Dean continues to drive recklessly at 110 miles per hour, almost getting into a five-car crash on a small bridge in Illinois. Sal has a vision of a jazz clarinetist who recently died in a car crash in Illinois. As they pull into Chicago, Sal again compares the group to gangsters coming from LA to "contest the spoils of Chicago." Once they get to their destination, Sal realizes they made it from Denver to Chicago, not counting the accidents and the stop at Ed Wall's ranch, in only seventeen hours.
In Chicago, Sal and Dean freshen up at a room in the YMCA and then head out to see the sights of the town. They follow a jazz band, and Sal recounts a brief history of jazz up to his present day. They follow the band to a different bar and listen to them until nine in the morning, taking only brief intermissions to get back in the Cadillac and try to pick up girls. Back at the bar, Sal and Dean listen to George Shearing, the musician Dean had named "God" in San Francisco. After Shearing, the jazz band realizes there is nothing left to play, but they try anyway. In the morning they return the Cadillac, dirty and busted, and get back to Chicago quickly before anyone can complain.
On a bus to Detroit Sal talks with a lonely country girl who has no plans for her life, nor does she know what plans her family has. Sal decides the girl is lost. In Detroit they sleep in an all-night movie theater. Sal becomes sick of life, deciding he is nothing more than a piece of garbage in the theater. In the morning they get a ride with a family man at the travel bureau who charges them four dollars a piece for the ride to New York. They drive overnight and in the morning get to New York. They go to Sal's aunt's new flat on Long Island, where they stay. They go to parties in New York. At one party, Sal introduces Dean to a woman named Inez. They have a quick affair from which she gets pregnant. The section ends with Inez and Camille both giving birth to Dean's children, albeit in different cities. Dean now has four children all over the country and no money. Sal and Dean decide not to go to Italy after all.
Sal's and Dean's philosophy of life, which took a greater form in the first chapters of part three, is now unleashed into the world through their travels unlike it had been before. Dean's notion is to live as spontaneously as possible in order to ignore, or transcend, the worries and responsibilities of life. Yet, as the two reach Denver, the consequences of living in such a way begin to confront them.
In Denver, Dean begins to try to satisfy whatever urge or lust comes into his mind. As they begin drinking heavily, Dean's lust causes him to stalk a young neighbor. The mother of the girl greets the two with a shotgun while a group of boys are ready to fight them, and Sal has to talk their way out of the mess. Dean begins stealing cars and eventually steals the wrong car, the car of a police detective, and by the time they are leaving Denver, Sal realizes that once again, things are a "mess." As they leave Denver, running from enemies and the police, Kerouac seems to be urging the reader to approach Dean's philosophy of life with caution.
When Dean and Sal get the Cadillac limousine that will carry them to Chicago, Kerouac begins using metaphors that echo Melville's Moby Dick. As Dean drives madly across the Midwest, Sal compares him to a "mad Ahab at the wheel." Like Moby Dick, On the Road is a first-person narrative about an extraordinary journey that takes place on the fringes of American society and deals with race and companionship.
In Detroit, Sal comes to face his own identity. Broke and tired at the movie theater, Sal's dreams and images of Hollywood play all night, beginning to merge and form together in his consciousness. It is in the movie theater where Sal notices the most "beat" of all the characters in the novel, in a sense-the homeless and destitute of Detroit-and the juxtaposition of the false reality of Hollywood and the true reality of this underbelly of America contrast sharply. Sal begins to identify most closely with the "garbage" he sees around him. He feels completely rejected by society and no better than the trash that litters the theater. Unlike the New York intellectual crowd that characterized "beat" at the beginning of the novel, this scene most fully identifies what Sal (and thus Kerouac, it seems) has come to view as the true "beat" culture of America.
The remaining journey to New York is uneventful, and Sal arrives back at his aunt's house, the constant haven for food and shelter. Dean does not seem to change; he again continues his own journey, finding another woman and having another child. As the section ends, Sal muses on Dean's responsibilities and the children Dean fathered all over the country. Part Three ends with a note of sadness in realizing the consequences of constantly living in the moment. But, true to himself, why should Dean worry about the consequences?