In the fictional town of Bayonne, Louisiana, the narrator, Grant Wiggins, attends the trial of Jefferson, a 21-year-old man who has been charged with the murder of a white storekeeper. Jefferson insists that two of his acquaintances, Brother and Bear, shot Alcee Gropé, the storekeeper, and the evidence seems to corroborate this. Jefferson's lawyer points this out, but rests his argument on the idea that Jefferson was too stupid to commit the murder, and executing him would be a waste of time because he is nothing more than a hog. Nevertheless, Jefferson is convicted and sentenced to death.
Grant is a schoolteacher and lives with his elderly aunt, Tante Lou, in the quarter, a poor black community thirteen miles away from Bayonne. Tante Lou is best friends with Miss Emma, Jefferson's godmother. The day after the trial, Miss Emma asks Grant to visit Jefferson in prison, hoping that he can teach her godson to walk with dignity before he dies. Although Jefferson is reluctant to get involved, Tante Lou insists he cooperate. Miss Emma appeals to Henri Pichot, a local plantation owner who is married to the sheriff's sister, to allow Grant to visit Jefferson. He receives Emma coldly but agrees. Grant's girlfriend, Vivian, further encourages him to teach Jefferson.
Henri Pichot introduces Grant to Sheriff Guidry, who remarks that Grant is "too smart for [his] own good" (49) because he uses perfect grammar and is highly educated. The superintendent of the county school district visits Grant's classroom, but seems out of touch with Grant's lack of money and books, and complains that the students have poor hygiene. While watching some of his older students chop wood, Grant reminisces about his own schoolteacher, Matthew Antoine. A bitter mulatto, Matthew advised all of his students to leave the South so that they could prosper and avoid violent deaths. However, Matthew was afraid to leave the South himself, because there he had a small degree of social cachet due to his mixed blood.
On Grant's first few visits with Jefferson, he is annoyed by the prison's stringent search procedures and segregated bathrooms, which he feels are degrading. Worse, Jefferson refuses to speak to Grant or Miss Emma. One day, Miss Emma pretends to be sick so Grant has to visit Jefferson alone. Jefferson's behavior is worse than ever; he crawls on all fours and eats like an animal, chanting that "I'm a old hog they fattening up to kill for Christmas" (83). Grant heads to his favorite bar, the Rainbow Club, and hears some locals talking about Jackie Robinson. He ponders the importance of heros to people in the quarter, thinking back to a story he read in college, James Joyce's "Ivy Day in the Committee Room," from Dubliners. At the time, he did not understand the story, but now he understands that it is about how much people value public figures. Grant tries to persuade Vivian to elope with him, but she cannot because she has not legally divorced her previous husband, with whom she has two children.
Grant returns to Tante Lou's house, to find that Tante Lou, Miss Emma, and Reverend Ambrose have waited up for him. They accuse him of lying about how much progress Jefferson has made, and Ambrose badgers Grant about having abandoned Christianity. The next day, Vivian comes to visit Grant in the quarter. They go for a walk in the sugarcane fields and have sex there; it is suggested that they conceive a child. When they return to Tante Lou's house, Grant introduces Vivian to Tante Lou and her friends as the woman he will marry, to Vivian's delighted surprise. Although Tante Lou is suspicious at first, she eventually judges Vivian to be "a lady of quality" (116).
On his next visit to the prison, Grant gets to know Deputy Paul Bonin, who is more sympathetic to Jefferson than the other police officers. Grant reprimands Jefferson for making Miss Emma cry with his obstinacy, but Jefferson only responds by saying rude things about Vivian and threatening to scream. As Grant leaves, Sheriff Guidry pulls him aside and tells him that Tante Lou and Miss Emma have requested that Jefferson meet with them in the dayroom, since his cell is too small to fit them all. The sheriff agrees, provided Jefferson wears shackles in the dayroom.
Jefferson continues to show little progress, but Grant perseveres due to Vivian's encouragement. At Grant's school, the children hold a Christmas pageant dedicated to Jefferson. Reverend Ambrose leads the opening prayer, directing it pointedly at non-believers (meaning Grant).
Two months later, a date is set in April for Jefferson's execution. This angers Grant, but he is unable to bring the news to Miss Emma, allowing Reverend Ambrose to do it instead. At Grant's next visit to Jefferson, the young man seems to have improved somewhat, and he has a civilized but sad conversation with Grant, expressing his wish for a gallon of vanilla ice cream. Grant gives Jefferson news of the people in the quarter, and promises to bring him a radio the next time he comes.
Grant gets the money for the radio from Joe and Thelma Claiborne, the owners of the Rainbow Club. Jefferson is very happy to receive it and plays it all day, but Tante Lou and Reverend Ambrose are furious at the new "sin box." They believe it turns Jefferson away from God and makes him reluctant to spend time with them. Grant argues with them, insisting that the radio is helping Jefferson to behave civilly. Grant brings Jefferson some pecans from his students, and asks him to be kinder to Miss Emma. Jefferson agrees, and tells him to thank the children for the pecans.
After some prodding at the next visit, Jefferson eats some of Miss Emma's gumbo even though he is not hungry, his first act of consideration for another person. Grant explains to Jefferson that a hero is someone who puts the welfare of others before himself, and that Jefferson must be a hero to prove to white people that they are wrong about him. Jefferson is moved by the speech.
Grant goes to the Rainbow Club and brawls with some mulatto bricklayers there, who are loudly complaining that Jefferson has made things worse for all "colored" people. The fight ends when Joe Claiborne knocks Grant out with the butt of a rifle. He wakes in Vivian's arms but refuses to acknowledge that he's done anything wrong, much to Vivian's exasperation. They argue but quickly reconcile. The next morning, Reverend Ambrose comes to visit Grant, and tells him that despite his education, he is naïve about how much Tante Lou suffered to put him through college.
Grant visits Jefferson, and finds that he has been writing his thoughts down in a notebook that Grant gave him. He urges Jefferson to pray, since it will make Miss Emma happy and might give him some peace of mind, although Grant himself is a non-believer. Jefferson is very afraid of death and wonders what his execution will feel like. The novel then switches from Grant's narration to "Jefferson's Diary," which is written with very flawed grammar and spelling. It includes memories from his childhood, as well as musings about dignity and whether God prefers white people to black people. From the diary, we learn that Grant has had the schoolchildren and many townspeople come to visit Jefferson, and Jefferson is deeply touched by their concern for him.
The eve of Jefferson's execution arrives. He has Miss Emma's fried okra for his last meal, and is unable to sleep. Instead of describing the execution directly, Gaines includes the reactions of many townspeople who do not appear elsewhere in the novel, emphasizing Jefferson's status as a public hero. Reverend Ambrose witnesses the execution, but Grant does not have the courage, and instead goes to work, telling his students to pray at the approximate time the execution will take place. Deputy Paul comes to visit Grant after the execution has happened, delivering Jefferson's diary and informing him that Jefferson faced his fate with great strength and dignity. He adds that he hopes to stay friends with Grant, and one day he would like to read Jefferson's diary if Grant thinks it's appropriate. Grant solemnly thanks him and returns to teach his class.