The sharecroppers recall the devastation of their native Oklahoma lands, brought about by drought and economic depression.
Having been released early from prison on parole for good behavior, Tom Joad meets up with Jim Casy, a lapsed preacher. When they get to the deserted and destroyed Joad family farm, they discover that the bank has foreclosed on it.
Tom and Jim decide to accompany the family to California, where fruit picking jobs are supposed to be plenty. Al Joad buys an old truck, and the family loads up the few possessions they can take. Connie and Rosasharn dream of a new life and home for Moses, their unborn baby. The next day the Joads bury Grampa, who has died during the night. The family then continues their journey down Route 66.
At a diner, the Joads experiences contempt from the truckers and waitresses when they try to buy only the food they can afford, but the diner owner and waitress decide to act out of compassion. Crossing the Mojave, Granma dies during the night, but Ma keeps her death a secret until they get to California. At the Endicott Farm, the scene flashes back to 1849, when George Endicott plants his first plum tree. In the present time, growers inform the Joads that there’s no work there. Another flash to 1924: George Endicott, the grandson, has become a successful businessman. Back in the present, the locals rally – with the influx of Okie laborers, their wages have been slashed. Nearby, plums are being burned, rather than being given to the hungry croppers. The Joads continue on to a Hooverville – a squalid shantytown. Ma struggles to keep the family together. Connie regrets leaving Oklahoma and storms off, never to return. The next day, the Joad men get involved with unscrupulous contractors. A woman is killed in the struggle, and Tom knocks a deputy unconscious, violating parole. Casy volunteers to stay behind and take the blame as the Joads escape to the truck. Noah Joad, feeling himself a burden on the family, goes to the creek and drowns himself.
Newly relocated at a clean, self-policing government camp, the Joads feel like people again. Local farm owners send in agitators to cause a fight during a hoedown so they can close down the camp, but the croppers remain peaceful. Pa persuades the Joads to go to a new farm. They realize that they have been brought in as scabs, triggering a riot outside the camp. Tom meets up with Jim Casy, now an agitator for farm workers’ rights. When Casy is bludgeoned to death by a deputy, Tom kills him and goes into hiding. The remaining Joads find work picking cotton and taking shelter in a boxcar. During the rainy season, Rosasharn goes into labor, but delivers a stillborn child. Ma asks Uncle John to go bury Moses while Rosasharn recovers to ease her pain; Uncle John instead chooses to cast Moses’ dead body into the river so that everyone can see “the fruits of their blindness.” The raging river has flooded the remaining Joads out of their home. The truck is swept away in the water, and Al is lost when he goes after it. Ma, Pa, Ruthie, Winfield, and a very weak Rosasharn seek refuge in a barn, where they find a boy and his starving father. Ma intuitively knows what Rosasharn must do, and ushers everyone else outside. Rosasharn nourishes the starving man with milk from her breast.