Nine-year-old Cassie Logan heads to the first day of school with her brothers, twelve-year-old Stacey, seven-year-old Christopher-John, and six-year-old Little Man. It is October, 1933, and they are the children of an African-American couple living in rural Mississippi. The family owns four hundred acres of land, half of which is mortgaged, and Papa must work half the year on the railroad far away to pay for it. Mr. Granger, whose family owned the land during slavery times, wants to buy it back and constantly threatens to coerce them into selling it to him.
On the way to school, TJ Avery and his younger brother, Claude, tell the Logans that the Berry family were burned by the white Wallace brothers. A white boy, Jeremy Simms, joins them for part of the walk. He goes to Jefferson Davis County School while the Logans attend Great Faith Elementary. At school, Cassie and Little Man get in trouble with the teacher, Miss Crocker, by protesting that their used textbooks list the condition "very poor" next to their race. Mama, who is a seventh-grade teacher, pastes paper over the inside covers of her students' books to hide this information.
Papa returns unexpectedly from the railroad with a very big, strong man named Mr. Morrison, who got in a fight with some white men and lost his job on the railroad. He will be staying with the Logans.
In October, the children must walk to school in the rain and mud and are splashed by the vindictive driver of the white school's bus. (The black school cannot afford a bus because the county does not give it enough money.) One day, after being forced off the road into a muddy ditch, Stacey leads his siblings in digging a trench across the road at lunchtime to make it look like the road has washed out. After school, they watch from the forest as the bus drives into the ditch, breaking its axle, flooding its engine, and leaving the white students without a bus for two weeks.
Later, the children hear that the "night men" are out. Cassie sees cars approach the house in the middle of the night and then turn around. Later, TJ tells the Logan kids that these men tarred and feathered a black man, Sam Tatum, for accusing Jim Lee Barnett, who owns the Mercantile in the neighboring town of Strawberry, of cheating him.
Stacey takes the blame when he is caught with TJ's cheat-notes during a test. He follows TJ to the Wallace's store, where he has been forbidden to go, and punches him. Mr. Morrison catches him and brings him home. Stacey confesses to Mama, who punishes the four children for going to the store by taking them to see Mr. Berry, who is burned so badly that he is not recognizable and can no longer speak. Mama begins to arrange a boycott of the Wallace and Barnett stores.
Big Ma takes Stacey, Cassie, and TJ to the market in Strawberry. While Big Ma talks to Mr. Jamison, a friendly white attorney, TJ admires a pistol in the main store. When Mr. Barnett waits on white customers while ignoring TJ, Cassie tries to remind him of their presence. He calls her a "little nigger," then throws her out of the store for arguing with him. In the street, Cassie bumps into Jeremy's sister, Lillian Jean, and is forced by Mr. Simms to say, "I'm sorry, Miz Lillian Jean," as Big Ma looks on.
Uncle Hammer comes to visit for Christmas, hears this story, and is only prevented from going after Mr. Simms by Mr. Morrison. Mama explains to Cassie that Big Ma had no choice but accede to Mr. Simms' wishes. Uncle Hammer drives the family around in his new Packard and also gives Stacey a new coat. TJ makes fun of him because it is so big on him until Stacey gives it to TJ to borrow until he grows into it. Uncle Hammer makes him give it to TJ permanently for being irresponsible enough to let TJ take it from him in the first place. On Christmas, Mr. Morrison tells the story of how, when he was six years old, his entire family was killed when an angry white mob attacked his house, where two young men accused of molesting a white women were hidden.
Big Ma puts the land in Hammer and Papa's names to protect it. Mr. Jamison agrees to provide credit for the families who have agreed to have Papa shop for them in Vicksburg rather than patronize the Wallaces' store. Mr. Granger, who owns the land upon which Wallace store sits, threatens Uncle Hammer and Papa with the loss of their land.
Cassie pretends to be friends with Lillian Jean, acting subservient, calling her Miss, and carrying her books for her. One day she takes her into the woods and fights with her, pulling her hair until she apologizes for the incident in Strawberry. Cassie threatens to tell the secrets that Lillian Jean has shared with her if she says anything to her father. Mama fails TJ on a test for cheating. In retribution, he mentions to the Wallaces that she has covered the inside of the books. Kaleb Wallace, Harlan Granger, and another man from the school board come to Mama's class when she is teaching a lesson about the injustices of slavery and fire her.
Stacey stops being friends with TJ, and TJ starts hanging around with RW and Melvin Simms, who are older and are white. Mr. Avery, Mr. Lanier, and several other people stop buying goods in Vicksburg when Mr. Granger and Mr. Montier raise the percentages of cotton they want from their sharecroppers and threaten to kick anyone who continues the boycott off their land. On the way back from a trip to Vicksburg to buy goods for the few families still participating in the boycott, Papa, Mr. Morrison, and Stacey must stop when the back wheels fall off their wagon. As they fix them, the Wallace truck stops behind them and someone shoots at Papa, grazing his temple. The horse tries to run away, and the wheel of the wagon rolls over Papa's leg, breaking it. Mr. Morrison fights off the Wallaces, badly injuring them.
With his new injury, Papa can't go back to work on the railroad, but it looks like the family might scrape by until the bank calls in the note on their mortgage. Uncle Hammer sells his Packard to pay for it. He brings the money to his brother's family on the week of the revival, a religious and social event, but must leave quickly so as not to incite further tensions. TJ shows up at the revival with RW and Melvin, who he says will buy him the pistol at the Barnett store. When Stacey and everyone else ignore him and enter the church, TJ is upset but finally leaves with the Simms brothers.
That night, thunder rolls and Mr. Morrison keeps watch outside the house. TJ taps on the door in the middle of the night and tells Cassie and Stacey that he broke into the Barnett Mercantile with RW and Melvin to steal the gun. When Mr. Barnett came down to investigate the noises, RW and Melvin, who were disguised with stockings over their faces, hit him with the flat side of an axe. When his wife came down, they threw her against a stove, knocking her out. TJ threatened to tell the police, so the Simms boys beat him up badly. He asks Stacey to help him get home, and all four Logan children end up walking TJ back to his house in the middle of the night.
The Logan children watch from the woods as the Wallaces, Simms brothers, and other whites break their way into the Avery house and drag out its inhabitants, beating them. Many of them call for hanging TJ, Mr. Morrison, and even Papa. Mr. Jamison arrives and tries to stop them. Stacey sends the other children home to tell the adults what is happening.
After hearing the story from Cassie, Papa sets off with his shotgun and Mr. Morrison. Soon, Mama notices smoke coming up off the cotton, which is burning. She and Big Ma go out to fight the fire, which is heading towards the woods. Before dawn, Jeremy Simms comes to the house and says that all the white men (whom Cassie and her brothers saw at the Averys' house) have gone to fight the fire. He has also seen Papa and Stacey, who are all right. Just then, it begins to rain heavily, which puts the fire out.
Cassie and Little Man rush to the cotton fields where they see white and black men and women putting out the rest of the blaze. Mama and Big Ma take them and Stacey home. There, Stacey tells Cassie that Mr. Jamison tried to stop the hanging, but Mr. Granger would not cooperate until he smelled smoke and sent the men to fight the fire. That is when Mr. Morrison (strangely, not Papa) went to get Stacey in the woods. Cassie realizes that the lightening didn't start the fire, but rather, Papa started it. Papa and Mr. Morrison arrive home and Papa tells Stacey and Cassie that TJ is with the sheriff and will probably be put on the chain gang where he might die. Stacey bursts into tears and runs off. Papa follows his son after putting Cassie to bed. In bed, Cassie cries for TJ and the land.