After hunting rabbits with a pistol, three African Americans—David Thomas; his fourteen-year-old brother, Joshua Thomas; and a friend—drive back to the city. David and the friend drop Joshua off at his parents’ home, then stop at a gas station. While David sits in the car, the friend robs the clerk inside. Charged as an accessory to armed robbery, David accepts a plea and receives a sentence of one year to life in prison, but various infractions extend his time. After three years, David is transferred to Mendocino State Prison, where he joins the segregated black population on the top tier of a cell block. At his first meal, David learns that blacks are the last ones in the mess hall, and when he pushes away his tray because the food is cold, fellow prisoners tell him to get used to it. David works in the prison print shop, which is run for profit but does not pay the prisoners. Meanwhile, David's brother Joshua visits a local university to ask a black activist professor, Paula Jones, to expand her political science classes and community outreach to prisons, complaining that his brother should have been on parole two years ago. Meanwhile, David plays cards with his new cell mate, Walter Nance, who admonishes David for not focusing his anger or knowing who he should be mad at. Walter gives David books written by black sociologist Frantz Fanon, revolutionary Che Guevara, black militant Malcolm X, and others, insisting that David needs to educate himself. Walter is biding time because he is scheduled for parole in eight months. Late that night, dozens of white guards storm the tier, pull the sleepy inmates out of their cells, and submit them to rectal inspections. Later, with his anger boiling over, David sits on the white side of the aisle during a movie and provokes a fight that results in his transfer to solitary confinement with Walter and three other black inmates. When guards pull David and Walter out of their cells to take a shower, David says aloud what Walter already knows: his upcoming parole has been rescinded. When guards push the inmates back to their cells, Walter resists and is beaten to death. Officer McGee, the head guard, calls David and the three other prisoners to his office and cajoles them, saying they will get a good report in front of the parole board if they do not mention Walter’s death as anything but a suicide. However, when David returns to the general population, he publishes a small, handwritten bulletin in the print shop called The Underground that describes Walter’s murder. When Joshua visits, David slips his brother a rolled-up Underground through the wire barrier, and Joshua delivers the paper to Paula Jones. She assembles a “citizen’s committee,” including African American Senator Billings, and travels to Mendocino State Prison to meet with the warden. David anticipates their arrival by hiding copies of The Underground in the paper towel dispensers in the civilian bathrooms. The pamphlet alerts the committee members that black prisoners are boycotting the cold meals and the prison jobs. As Paula passes David’s cell, he calls her name, shows that he is reading her book, and tells her he is Joshua’s brother. After the committee leaves, McGee gathers his guards, shows them a copy of The Underground, and orders them to use their “snitches” and midnight shakedowns to find out who printed it. Tipped off by informer Art Horton, McGee throws David and Lewis, his new cell mate, into maximum security. Paula, meanwhile, uses her political influence to visit David and is given permission to record their conversation. David is brought in chains to a small room with a window so that a guard outside can watch them. Paula says she has read David’s prison letters and feels the depths of his humanity, but she worries about Joshua’s youthful rage. Later, she plays her taped conversation with David to the citizen’s committee and convinces the warden to return David and Lewis to their regular cell. McGee announces that black and white inmates will now exercise together in the yard, but several white prisoners taunt the blacks and warn them to stay on their own side. When Lewis is deliberately tripped, he attacks the white inmate and is shot to death by a sniper in a guard tower. Later, when the black prisoners hear on the radio that a grand jury determined that Lewis’ death was “justifiable homicide,” they chant “Murder” and throw their belongings off the third tier. As guards rush to stop the riot, one is pushed over the rail to his death. McGee arrests David, Willie Robinson, and Marty Williams for the murder and has the three prisoners taken to solitary confinement. McGee pulls two white, vulnerable young men, the Davis brothers, out of the general population and tells them they can have their own cell and special privileges if they testify in court that they saw the three black men throwing the guard over the rail. Outside, Paula leads demonstrations in a campaign to “Free the Mendocino Brothers.” Returning to the prison, she tells David she wants to publish his letters and The Underground, but she is afraid that the revelations will make his life in prison harder. David insists that she publish them anyway, but is concerned for her safety, because black leaders have a history of being “cut down.” He suggests that she hire Joshua to protect her. Paula buys a pistol at a gun shop and gives it to Joshua. At the trial, a lawyer for the Mendocino Brothers brings up several motions, including a venue change, but the judge denies them all, and when David hits an abusive deputy and is dragged from the courtroom, Joshua pulls his gun, takes both the judge and the district attorney hostage, and announces that they are going to a radio station to tell the truth about the Mendocino Brothers. After Joshua commandeers a van outside, he and his two captives are killed in a crossfire. Knowing Joshua’s gun will be traced to her, Paula goes underground, but FBI agents track her to Chicago, Illinois, and return her to California. Meanwhile, the Davis brothers confess their deal with McGee to the warden. In a desperate attempt to create a diversion, McGee fakes a bomb threat and moves all the cell block inmates to the laundry area for their protection. Art Horton pulls out two pistols and announces that it is time for the inmates to take over the prison, but David knows that McGee has set them up to be murdered. When Horton confesses that McGee gave him the guns, David warns the others that the guards are waiting to kill them all, black and white, the moment they leave the laundry. To avoid a massacre, David takes the two guns, grabs a guard outside, and runs him across the yard. McGee opens fire, killing the guard, and David shoots McGee moments before snipers in the towers kill him. The white prisoners join the black prisoners in a boycott to protest David’s death and the institutional brutality.