In southern 1940s Louisiana, near the town of Bayonne, a young black man named Jefferson is tried for the murder of an old shopkeeper, Alcee Gropé. The white prosecutor accuses him of accompanying two other black men to murder Gropé, stealing Gropé’s money, and celebrating by drinking a bottle of whiskey. The defense attorney, also a white man, argues that Jefferson was in the wrong place at the wrong time: the two killers gave him a ride into town, and he was caught in a shootout. Ultimately, the defense attorney urges the jury, twelve white men, to spare Jefferson’s life on the basis that he is black and poor, and killing him would be like killing a hog. Nonetheless, the jury finds Jefferson guilty and sentences him to death, at a date to be determined later.
The novel’s narrator, Grant Wiggins, is a black schoolteacher who lives with Tante Lou, the aunt who has raised him since he was a child. Lou is a close friend of Jefferson’s grandmother, Miss Emma Glenn, who has raised Jefferson since he was a baby. Though Emma says that Grant needn’t do anything he doesn’t want to do, Lou insists that Grant visit Jefferson in his jail cell and teach him how to die like a man, instead of a hog. Grant refuses on the grounds that Jefferson is basically already dead, but Lou is so persistent and forceful that he agrees to help her negotiate with the sheriff to allow Jefferson to have visitors. Emma, Lou, and Grant go to the house of Henri Pichot, a wealthy white man for whom they used to work, and ask him to allow Jefferson visitors. Pichot responds irritably that he will speak to the sheriff. Several days later, Pichot summons Grant to his house, where Pichot and Sheriff Sam Guidry, both of whom are highly bigoted against blacks, tell Grant that he can visit Jefferson, but that he mustn’t cause any trouble.
In the weeks leading up to Grant’s first visit, he continues teaching first through sixth-graders at the segregated school he runs in the local church. Winter is coming, and the community is going through the annual practice of sending kindling to the schoolhouse so that it can stay warm for the cold months. As Grant watches old men deliver wood, he thinks to himself that his students will end up working just like these men and never use any of the knowledge he’s giving them. He thinks back to his childhood, when he was a student at the school where he’s now a teacher. Grant fears that he’ll end up like his old teacher, Matthew Antoine: cynical, disillusioned, and left with nothing to show for a lifetime of teaching others. Grant spends many of his afternoons with his beautiful girlfriend, Vivian Baptiste, at the Rainbow Club in nearby Bayonne. Vivian is still married, and has children, but she is in the process of separating from her husband. She and Grant are very much in love.
During Grant’s earliest visits to Jefferson, he’s accompanied by Tante Lou and Miss Emma. Jefferson is almost completely unresponsive, even though Emma has cooked him delicious food, and his silence causes Emma great pain. Grant becomes familiar with the process of visiting Jefferson: he’s searched, sometimes mocked by Sheriff Guidry for believing that he can teach Jefferson anything, marched past the other prisoners, and then given an hour to speak to Jefferson. On Grant’s first visit alone to Jefferson, he brings Jefferson Miss Emma’s food, and Jefferson eats it like a hog and says that he’s being fattened up like an animal before he’s slaughtered.
For the next month, Grant continues to visit Jefferson, though these visits are almost as unproductive as the first one. Grant notices, though, that while Jefferson doesn’t talk, he’s desperate for Grant’s company. Grant also develops a friendship with Paul Bonin, the young white deputy who often escorts him to Jefferson’s cell. While Paul is white, he doesn’t disrespect Grant or Jefferson.
Tante Lou, Emma, and the community’s minister, Reverend Ambrose, convince Sheriff Guidry’s wife, Edna Guidry, to convince the sheriff to allow them to visit Jefferson together, meaning that they have to sit in the jailhouse’s dayroom rather than in Jefferson’s cell. Meanwhile, Grant introduces Vivian to his family, and we learn that Grant doesn’t attend church anymore, causing great pain to Tante Lou, who, like nearly everyone in the community, is Catholic. Tante Lou is polite around Vivian, but she is displeased to hear that she is getting divorced, and tells Vivian to remember God. Afterwards, Grant tells Vivian that he doesn’t know what he’s doing with Jefferson, and suggests that they move to another city, far away. Vivian refuses to do so, reasoning that she cares too much about the children she teaches. She also encourages Grant to continue talking to Jefferson, suggesting that Jefferson is changing, even if he doesn’t seem to be.
In December, Grant puts on the annual school Christmas play, which the entire community attends. Though everyone has donated food and clothing to the play, and enjoys singing Christmas songs, Grant is privately depressed, since he organizes the same show year after year, never seeing any change. Then, in early February, Grant learns from Henri Pichot that the judge has set a date for Jefferson’s execution: the second Friday after Easter. With Vivian’s support, he offers Miss Emma his comfort and support, and she tells him that he and Ambrose must make Jefferson a man before he’s killed.
On his next visit to Jefferson’s cell, Grant learns that Jefferson would like a radio so that he has some form of entertainment while he waits to die. He buys a radio, borrowing money from the owner of the Rainbow Club, Joe Claiborne, and gives it to Jefferson the next day. Reverend Ambrose is furious that Grant has given Jefferson a “box of sin,” but Grant insists that Jefferson needs to take his mind off his death. On his next solo visit to the jail, Grant brings Jefferson a bag of pecans that his students have gathered, and tells Jefferson that he’s going to give him a notebook and pencil so that Jefferson can write down his thoughts. At the end of this visit, Jefferson stands up and tells Grant to thank his students for the pecans. Grant senses instantly that he’s made a “breakthrough.”
Shortly after his breakthrough, Grant, Tante Lou, Reverend Ambrose, and Miss Emma visit Jefferson together in the dayroom. Miss Emma has made a large pot of gumbo for the visit, but Jefferson refuses to eat any of it. Grant and Jefferson slowly pace around the room. As they walk, Grant tells Jefferson that he must be a hero—more of a hero than Grant himself could ever be—and stand up to the racist whites who have sentenced him to death by being brave and strong. He says that Jefferson must be good to Miss Emma by eating some of the gumbo she’s made him; Jefferson sits down and eats some of the gumbo, bringing joy to Miss Emma.
Later, Grant celebrates in the Rainbow Club, and gets into a fight with two "mulattoes" (men of mixed race) who think that Jefferson should have been executed long ago. Vivian takes Grant back to her home, where Grant tells her that he loves her and needs her support while he visits Jefferson. Vivian suggests that Grant doesn’t know what love is, and Grant is about to leave when he realizes that he has no one else to turn to—he goes back inside Vivian’s house and embraces her.
Only a few weeks before Jefferson is to be executed, Reverend Ambrose visits Grant and tells him that he is endangering Jefferson’s soul by giving him a radio and never mentioning Heaven. This leads to a heated argument between the two of them, in which Grant says that he believes in God but not in Heaven. Ambrose replies that he’s had to lie to his congregation, filling their heads with hope and optimism. Grant is a fool, he concludes, for not understanding that people need hope and Heaven to be strong. On Grant’s next visit to Jefferson, he tells Jefferson that he doesn’t believe in Heaven, but that God says that humans must be good to one another.
The following chapter consists of excerpts from the notebook Grant gave Jefferson to use as a diary. In broken English, Jefferson writes that Henri Pichot and his friend gave him a penknife; though Jefferson is unaware of this, we understand that Pichot has made a bet that Jefferson will kill himself before he’s executed, and gave him the penknife as a potential weapon of self-harm. Jefferson also writes about saying goodbye to Miss Emma. He concludes by thanking Grant for teaching him, noting that no one else has ever been so good to him.
The next chapter is written from the point of view of various characters who witness aspects of Jefferson’s execution. Reverend Ambrose prepares to read Jefferson the 23rd Psalm; meanwhile, black and white workers see a truck carrying an electric chair pull up to the courthouse. In the jail, Sheriff Guidry says that Jefferson must be shaved so that the electric chair will work. Paul arranges for him to be shaved. When Paul is about to leave Jefferson’s cell, Jefferson asks him if he’ll be there at the execution. Paul says that he will.
Grant doesn’t attend Jefferson’s execution, but he leaves his classroom, telling his students that they must stay on their knees and pray until he receives news that Jefferson is dead. He walks outside and thinks to himself that he was wrong to disagree with Reverend Ambrose: Ambrose has far more strength than Grant will ever have, and this is because Ambrose believes in God and Heaven. Grant senses that Jefferson has been killed, and he goes back to the schoolhouse. As he walks there, he meets Paul, who has just come from the execution. Paul shakes hands with Grant and tells him that Jefferson was the bravest man in the room when he was executed. Paul says that Grant must be a great teacher; Grant replies that Jefferson taught himself. Paul gives Grant Jefferson’s notebook, and Grant walks back into the schoolhouse in tears.