The narrator relates a retrospective account of his life, beginning in the South with his graduation at the top of his high school class. Invited by the school board to give a speech on the virtues of humility, he is first forced to take part in a blindfolded brawl with nine other black students and then made to scramble across an electrified carpet, scooping up coins. Only after this humiliation is he permitted to make his speech and receive his scholarship to the State College for Negroes.
During his junior year at college, he is assigned by Dr. Bledsoe, the head of the college, to serve as chauffeur for a visiting white benefactor, Mr. Norton. At Norton’s insistence, the narrator stops the car so that Norton can talk to a local black farmer, who has fathered a child with his own daughter. The farmer’s story fascinates and upsets Norton, and he faints on the ride back to the college. Stopping for assistance at a local bar, The Golden Day, Norton and the narrator become embroiled in a melee between some local shell-shocked veterans and their keeper, who are regular clients. Norton is slightly injured, and this incident leads to the narrator’s suspension from the school, after a confrontation with Bledsoe in which it becomes clear that Bledsoe is not only a tyrant to his students but also an "Uncle Tom" to the white community.
Traveling to New York, the narrator carries a sealed letter from Bledsoe purporting to recommend him to potential employers; only after repeated disappointments does the narrator learn that this letter instructs its readers to give the narrator hope but, under no circumstances, a job. The narrator does finally find work in a paint factory, but on his first day, he has a fight with his supervisor, during which there is an explosion. When the narrator wakes up, he is in the company hospital and has apparently undergone an involuntary brain operation, possibly a lobotomy. Released from the hospital, he wanders the streets until he is taken in by Mary, who nurses him back to health.
Some time later, the narrator witnesses the eviction of an elderly black couple; angered by their victimization and frightened by the angry crowd, he makes a speech advising restraint. Somehow, though, his words bring on the riot that he had both feared and desired. He escapes, but the incident brings him to the notice of the Communist Brotherhood, which is looking for a spokesman in Harlem. His first speech for the Brotherhood, delivered at a rally in Harlem, is a tremendous success with the audience and with Brother Jack, the leader of the Brotherhood, but it alienates and frightens some of the Party members. Over the next few months, the narrator finds himself at the center of a power struggle within the organization, and when he gives an unauthorized interview to a magazine, he is moved out of Harlem and assigned to lecturing groups of white women on "The Woman Question." One of these white women, the wife of a Party official, seduces the narrator, hoping that he will fulfill her fantasy of being raped by a black man.
At about the same time that the narrator is reassigned, Tod Clifton, who has been a friend to the narrator, disappears from the organization; the narrator later finds him selling dancing sambo dolls on a street corner, but before he can find out what has happened to bring about this defection, Clifton is shot by a white police officer. At Clifton’s funeral, the narrator gives an exasperated speech, telling the many who have turned out to "go home and don’t think about him. He’s dead and you’ve got all you can do to think about you." The crowd ignores his words but understands his anger, and he leaves them in a state of "pent-up tension"—tension which contributes to, and perhaps causes, the apocalyptic race riot at the end of the novel.
The riot, which takes place in Harlem, is an extended and surrealistic scene, in which the violence that has been building up inside the narrator, and inside the community,is released. As blacks loot black businesses and burn their own homes and belongings, the narrator stumbles through the streets, watching what seems to be the end of the world. He is nearly executed by Ras the Destroyer, who accuses him of serving the white man’s purposes; he escapes but is chased into a manhole by some white vigilantes. Unable to climb out, he finds his way into an unused and forgotten basement apartment, where he takes up residence as an underground man. By the end of the novel, he has severed all his ties to the past, lost all of his illusions, and retreated into anonymity and invisibility. He claims that he is in hibernation, but it is not at all clear that he will ever be restored to action, or to the world.