The rains stopped coming to the Oklahoma fields. The land and its crops dried up, it started to release its topsoil. The dust which was formed settled into every crack and crevice in the homes, the fences, and the barns. This was how the Dust Bowl began in Oklahoma.

A man from Oklahoma City Transport Company is taking a break from driving by having a bite to eat at a diner. He is talking to the waitress and enjoying the company for a while. His life is a lonely one, because his company does not allow the men to have a radio or riders in the truck with them. He leaves and sees a man in a brand new suit out by his truck. The man is Tom Joad, he wants a ride to his father's place a few miles down the road. The truck driver points out the sign in his truck window, which states "No Riders". Tom is undeterred by this sign, he points out that a good guy who is not controlled by his boss would give him a ride and he thinks the truck driver is such a guy. The truck driver, not wanting to seem as a bad guy under the thumb of his boss, decides to give Tom a ride.

Once underway, the truck driver notices Tom's new clothes and comes to the only logical conclusion. Tom has just been released from prison. He starts to ask Tom questions about himself, under the guise of being friendly. But, Tom knows what he is really after and tells him he has just been released from McAlester, a prison, where he has spent the last four years serving time for homicide. Tom now plans to work with his father who is a cropper, because this way he will not have to lie to get a job.

After the trucker drops Tom off at the side of the road, Tom starts the walk to his parents' farm. As Tom Joad is walking home he spots a turtle and he decides to take it home to his younger siblings. He is tired and thirsty, so when he spots a lone tree in the distance he quickens his pace to reach its shade. He finds Jim Casey lounging at the base of the tree singing. Jim is a former reverend, who has fallen away from preaching. He is the man who baptized Tom and used to hold church meetings for the people of the area; now he indulges himself in whatever desires he has. He explains to Tom how he fell from preaching the Holy Spirit. He would, after every meeting, lay with a girl who was at the meeting, he would then feel guilty about his actions. He finally came to the conclusion that sin and virtue did not exist, but instead people were themselves. He felt a person's actions were their own and not based on a supreme being. This is how he justified his actions to himself.

Tom told Jim Casey he was imprisoned, because he beat a man to death with a shovel. The two men had been drunk at a dance and the man had knifed Tom. Tom in turn took a shovel to the other man's head and killed him. He was sentenced to seven years in prison, but was let out in four due to him exhibiting good behavior.

The two men decide to walk together to Tom's parents' house. Upon arriving there Tom sees that the place is no longer occupied.

Many people during this time lost their farms, because the banks decided it would be more profitable to replace the small farmer with machines to work the ground. The drought had left the small farmer with little or no crop, and because they tilled the land without the use of tractors, the amount of crops they could produce was greatly reduced. They were tenant farmers, which allowed the bank to come in and throw them off the land, if they felt it was necessary. This is what happened time and time again, the small farmer was replaced by the tractor which could farm more land cheaper and quicker than the farmer could. The farmers not only lost their land, but also their homes.

The Joad family homestead was deserted. Tom could not figure out what had happened to his family. He at first thought they had all died, but after thinking about it, he realized he would have been told if that had happened. Jim Casey and Tom saw someone walking at a distance towards the house. It was Muley Graves, a man Tom had known since he was a child, he told Tom about the loss of the farm to the Shawnee Land and Cattle Company. It seems they owned the land and threw the farmers off it in order to have their own farmers farm the land. They used tractors and planted every square inch of land. Tom's family is living with his Uncle John, until they make enough money chopping cotton to buy a car and move to California. The three men eat some rabbit together, until the local sheriff's deputy comes by and they have to hide to keep from being caught as trespassers. They decide to walk the eight miles to Tom's uncle's house the next morning. Jim Casey feels his new calling is to be of help to the people moving to California. Tom tells the men he can't move out of Oklahoma, because it would violate his parole.

The people of Oklahoma are going through the most difficult period of their lives. The Dust Bowl has made living in Oklahoma very difficult, if not impossible. They have been thrown out of their homes and off their land. They now have to find a way to travel to California and to make a better life for themselves. The Joad family is one of these families, but they have the additional problem of Tom's probation.