The story starts from a man of about thirty walking along the dusty road framed by corn fields of Oklahoma. His name is Tom Joad. After serving time in prison for an accidental murder he returns to his home, a farm in the middle of nowhere. He is released on parole, so he has no right to leave the state. He thinks about meeting his big family: grandparents, parents, three brothers and two sisters.
On his way tom meets his childhood preacher, Reverend Jim Casey and they continue to walk together. But no one of them knows that as soon as they arrive to the Joads’ farm, they both will have to leave it forever. The farmers are driven away from the land they care about - the land owners now get much bigger profit from leasing land to big companies with technic. One tractor deals with the big field faster than a dozen of farmer families.
People are ready to defend the land which they consider their own. But who they have to shoot? Tractor driver? Or the bank director who leased the land? The farmers are forced to obey. Horrified, Tom stands in his yard, looking at the empty abandoned house. His neighbor, who accidentally notices Tom’s return, tells the man that the Joads temporarily moved to Uncle John’s farm, preparing to leave elsewhere. Tom and Casey go there.
The family greets them both warmly and joyfully, they really missed Tom. The next day they all board an old truck and the family starts their journey. Reverend Casey is travelling with them too. They go to California hoping to find new home and work there, the advertisement flyers distributed everywhere promise that there is plenty of jobs available there. The track drives to a highway, joining the wide stream of refugee farmers from everywhere moving to the West.
The trip is hard. The truck is too small and old to offer sun protection for every passenger, so those who travel on top of it get heavy sunburns at the end of the very first day. Also one of their dogs is run over by another car and children are grieving him. Also Tom’s grandfather constantly complains about them leaving their house. He was so prone to stay that his grandchildren had to put sleeping pills in his coffee just to board him in. But his complains are understandable: he is too old to take such a hard changes easy and to endure the hard way under a scorching sun.
On their way the Joads meet another family - the Wilsons, husband and wife. Wilsons offer to make a camp and let the exhausted Tom’s grandfather to rest in their tent. Tom gratefully agrees, but unfortunately it is too late - the old man dies this very evening of sunstroke. The men bury him near the road without excessive mourning - they have to move on, both physically and metaphorically. Tom and his younger brother help the Wilson to fix their car and the two families continue their journey together.
It seems that the whole country is fleeing to the West like refugees of war. But even if they look like refugees, they are disciplined as an army. On their way they develop their own laws, rights and punishments. When one family stops, some other stop nearby to protect each other. The ones who have spare food feed the hungry ones. The chilled ones need to be warmed, the ill ones need to be tended. A family that lost someone finds a handful of coins near their tent at the morning. As the people move towards the Western states, their rules become more and more perfect and humane and their camps now resemble small towns, because all the travellers get more experienced. They start to think of themselves as of community, not a bunch of individuals trapped in the same situation.
But the Western state are not welcoming them. Actually their inhabitants are horrified with the crowd of people moving towards their land. Half a million people is on their way already and one million more is waiting to be driven away from their land, because tractors have already invaded their fields and the farmers aren’t needed anymore. The closer Joads are to California the more often they see people running in the opposite direction. They tell terrible things: the people from the East come in large numbers, the locals are hostile, there is not enough work so the wages are not enough even to pay for the food. But the refugees still believe in their Promised Land with white houses among green gardens as California is depicted on the advertisement flyers. Finally, having overcome all the difficulties of the long journey together, the Joads and the Wilsons make their way to California.
They crossed the mountains and now stay near the river. On the other bank of the river lies vast desert they have to cross - and this part of their way will be much more difficult than everything they survived through before. But suddenly their older brother Noah refuses to go any further, saying that he is fed up with this way to nowhere. He leaves down the river saying that he will never stay hungry with an unlimited supply of fish and water. The Joads have no time to get over this loss - the sheriff appears near the tents and tells the refugees to get out from here. The Joads now have to cross the desert at night without even seeing the way. The Wilsons can’t follow them - Wilson’s wife is too sick and isn’t able to go any further for now.
In the desert Tom’s grandmother also passes away. The family carries the body to the nearest city of Bakersfield and she is buried there at the public expense. The Joads arrive to Bakersfield with only forty dollars left, so they can’t give her a proper funeral anyway. They continue driving finally reaching the fertile lands. But the local people meet them owned with rifles and axes, ready to protect their jobs and property from the crowds of hungry refugees. But the company owners are glad to see newcomers: they will do anything to feed their children, working themselves to half-death just for food. People are treated like cattle by their employers and like parasites by their new neighbours. They slowly but steadily become enraged with such injustice.
The Joads still live in the refugee roadside camp they called Hooverville. Konny, the husband of Tom’s younger sister, Rose of Sharon, leaves the family and no one knows where he goes. Pregnant Rose is devastated by his departure. On this very day a man comes to Hooverville hiring people to harvest fruits. He is accompanied with local sheriff. One of the smartest inhabitants of Hooverville demands working contract and documents to read beforehand - he wants to be sure that they won’t be tricked into working for free again. But he is immediately accused of being a Communist and the sheriff tries to arrest him. A fight starts and, unfortunately, Tom is involved. To prevent Tom from having troubles with the police (he is still not allowed to move to another state) Reverend Casey says that it was he to blame. The sheriff takes Casey with him to prison, threatening to set the camp on fire next time. Joads have to leave again, they can’t risk that much. They move to the south to find another camp they heard about in Hooverville. The camp is called Weedpatch, it is built by government and it is rumored to be quite comfortable, with hot water and real toilets. But on their way there they encounter a gang of people who demands that the Oks (that is, the Oklahomans) must go away from their land. Tom turns the truck, choosing the long way to the camp, his mother can barely calm him down and persuade him not to start another fight. Tom is surprised with her serenity, but still listens to the woman.
The family reaches the camp that appears exactly as good as they heard of it. Finally the Joads can feel they are citizens, not slaves and cheap labor force. They can wash themselves and their clothes and have a good rest. But still there is no work for the refugees. People try to understand what shall they do to survive. Some of them persuade other to create an alliance and rely only on themselves, because the authorities and the locals are clearly against them. They are able to imprison and humiliate them one by one, but they will have to listen to them all as a community.
This year in California is a year of an extraordinary harvest. Branches bend under the weight of the fruits and the vines are covered with grapes. But the purchase prices are too low, the small farms can’t hire people to help them gather their harvest - because the work now costs more than the food. Only large companies can survive and they start to deliberately destroy part of the harvest to raise the prices. The crops are rotting, the smell of putrefaction covers the labor camps. Children, ill and elderly people start to die from malnutrition, while the piles of fruits are poured with gas and burned. Sacks with potatoes are thrown into the river and the police shuns away hungry people begging to let them have some. This is the time when the grapes of wrath start to grow in the souls of the refugees and soon they will ripen.
The Joads leave this camp also. In search for work they travel north. Suddenly the policemen on motorcycles block their way. Tom is frightened, but they are only offering them a job. The policemen escort the truck off the hallway to the other working camp. The whole family starts to work on collecting peaches. After the exhausting work for all the day their salary is barely enough to buy something to eat. The prices in the local shop are deliberately much higher than anywhere else, but the seller in the shop is the same wage worker as they are, so he can’t offer a discount. When Tom’s mother buys food, she hasn’t enough money to buy sugar and asks the seller if she can borrow some until tomorrow. The seller hesitates, but finally agrees, paying for her sugar and asking her to return him money tomorrow. Leaving, Tom’s mother tells him that she is sure that she should ask for help only poor people - the rich ones woudn’t understand her at all.
In the evening Tom goes out to wander around the camp and look for familiar faces. He sees a lonely tent at the outskirts of the camp and goes there just to find the preacher Casey sitting inside. Casey tells Tom about what he have seen in prison. He says that the prisoners are mostly decent people who committed crimes because of dire need and poverty. Reverend Casey also explains Tom that the previous working shift is striking because the wages were reduced to ridiculous amounts, so the policemen catch any other refugee they can find to be the involuntary strikebreakers. Casey tries to persuade Tom to speak with his fellow workers, so they too will join the strike. But Tom is sure that hungry people who finally received at least some work won’t do that.
Suddenly the men hear footsteps outside. Tom and Casey leave the tent and try to hide in the darkness, but they stumble upon a man armed with a stick. He looks for Casey, who appears to initiate the strike. Calling him a Communist bastard, a stranger hits Casey and the preacher falls dead. Insane from grief and anger, Tom starts a fight, beating the murderer with all his strength and fury. The body soon falls to his feet, but Tom’s nose is broken - now it is obvious that he fought someone.
The next day Tom stays in his tent. He learns from the chatter in the camp that the man he fought at night is dead and the police is now looking for anyone who is also beaten. With Casey’s death the strike is ended and the garden owner immediately halves the wages again. But even for these scarce money people are ready to fight.
Ten-year-old brother of Tom also gets sick from malnutrition. Rose of Sharon is almost in labor and the family have to find a good place to care for their weakest. They hide Tom among their possession at the bottom of the truck and leave the camp at night. They avoid highways, riding the country roads. The Joads drive all the day, finally stopping near the cotton farm where cotton pickers are needed. They stay there and start working. The cotton farmer is a decent man, the Joads’ wages now are enough for food and clothes. Tom still hides in the truck and his mother brings him food at night. But one day his little sister Ruth says that her big brother killed a man and now has to hide to the farmer’s kids she plays with. Nothing bad happens, but Tom realises that he is a danger for his family. He is going to leave and do the same that Casey did: become a defender of workers’ rights and raise them to fight for themselves, starting strikes and demanding the decent working conditions, treatment and payment.
The cotton picking season is ending, now there will be no work until spring. The family doesn’t have any money at all. The rainy season begins and the river floods the workers’ trucks. Uncle John and other men try to build a dam, but unsuccessfully, the rivers breaks through it almost immediately. While they are struggling, Rose of Sharon gives birth to a stillborn child. The mother decides that they have to leave and find a higher place where it is drier. After they drive along the road for the short time they see an old barn and go there to protect themselves from the pouring rain. They see a man, who is dying of hunger. The little boy, his son, begs in despair to save his father. Rose of Sharon, whose breasts are filled with milk lies down silently near the dying man and starts to breastfeed him.