In a dystopic future society, married couples are allowed to become pregnant only once and are not permitted to become pregnant again even if the baby doesn't survive gestation or delivery. A faceless corporation called MenTel controls society, including its prisons. Couple John and Karen Brennick have had one failed pregnancy and are forbidden to have another, however she becomes pregnant again. In the film's opening scene, the couple are attempting to pass a security checkpoint while travelling to Canada. Though they're careful to protect Karen's abdomen from detection, the guards become suspicious and try to stop them. Karen tries to run for the border but John is captured and sent to a MenTel prison. When another prisoner on the transport to the penitentiary asks John why he's smiling even though he'd been sentenced to 31 years, John says he's happy because Karen escaped.John arrives at the penitentiary, a vast underground facility where treatment is harsh and punishments are brutal. He is ushered through the initial check-in where a small device is forcibly inserted down his throat: an "intestinator", which causes extreme abdominal pain when a punishment order is issued. The device can also be triggered to detonate in cases of extreme punishment, which John witnesses soon after he & the other prisoners are implanted; a prisoner, who becomes hysterical and crosses a safe-zone, is killed when his abdomen explodes.John is put into general population with some of the prison's worst inmates. In the cell that he shares with three men a hulking man, Stiggs, lords over the cell. John is forced to sleep on the floor. During his first night, he dreams of a sexual encounter with his wife and is interrupted by the prison's control system, ZED-10, which can enter the minds of inmates who have inappropriate thoughts. The prison's director is a man named Poe, who oversees ZED's operations.John is sent to the construction zone of the prison where inmates are forced to work on expanding the facility. Gomez is attacked by a hulking inmate named Maddox, who has the code for murder, 187, tattooed on his forehead. Maddox attacks John, who holds his own briefly until Poe orders them to be intestinated. John, Maddox and Gomez are forced to stand for hours until one of them confesses to starting the fight. John confesses and is brought before Poe himself. Poe reveals that Karen was actually captured at the border and has been sent to the prison. John is further punished with intestination and sent back to his cell.The next day Maddox attacks John. Poe delays stopping the fight and the two men battle across the walkway that leads out of the cellblock. The walkway is retracted and John wins the upper hand, causing Maddox to fall off the walkway where he hangs on by one hand. John pulls the man up, saving his life, however, Poe orders a powerful weapon called the splattergun to target Maddox' intestinator: the man's abdomen is blown out and he falls to his death. John is immediately intestinated along with dozens of other prisoners at random. While John writhes in pain, he notices that Maddox' intestinator lies nearby, undamaged. As he's dragged away to isolation, he passes it to Gomez.Before he's punished, Poe allows John to talk to Karen. John is then subjected to physical and mental torture in isolation -- he is strapped to a Gimbal that spins him around relentlessly and feeds him hallucinatory visions that bombard his senses. After spending three days spinning, he's returned to his cell but is catatonic and remains in that state for four months. His other cellmate, Abraham, who works as a housekeeper in Poe's office and living quarters, nurses John. When it seems hopeless to return John to his normal state, John returns, having been encouraged by the thought of his wife, who had gotten Poe drunk on champagne and had accessed ZED, entering John's dreams and breaking his catatonia. John becomes leader of the cell, bumping Stiggs down the ladder, and receiving Maddox' old, prized bunk.While John was in isolation, D-Day had taken the opportunity to study the intestinator. He finds that they are magnetic; using Stiggs as a test subject, he uses the freed intestinator to pull the other one out of Stiggs. It causes Stiggs a great deal of pain and nausea but the men realize they can at least free themselves from ZED's & Poe's control. They also have Karen and Abraham steal a small crystal from Poe's office, part of a holographic projector which shows construction plans for future prison levels. John forms a plan to have the men escape out of one of the construction sites where they all work. While they study the plans, they crystal is dropped and damaged. Abraham, who'd been up for parole, takes responsibility and may lose his chance at release. He decides to join John and the others in the escape, also realizing that he will never be granted parole anyway.Poe becomes attracted to John's wife Karen. He allows her to live in his apartment with her. One day she finds him in a reclining chair, hooked up by leads to ZED; Poe is a cyborg. Horrified, Karen rejects him. Poe also reveals a darker secret: any children taken from mothers who are imprisoned are given to Men-Tel researchers, who turn them into cyborgs like Poe. The plan is to replace the human race with enhanced people like Poe. Abraham, who'd been listening to their conversation, tells John, who charges Abraham with freeing Karen when the escape is attempted.The next day when the men report for work, John and Stiggs start a fight to distract the guards at the construction site. While they do, D-Day places all the intestinators he'd extracted from his cellmates on a ventilation pipe. In Poe's office, ZED, citing a small list of Poe's own violations of Men-Tel policies, orders him out of her control room when the fight breaks out. She orders the prisoners to be intestinated but when Poe hears her say Maddox' name, Poe pleads with her to let him have control again.When ZED orders the intestination, the intestinators placed by D-Day explode, blowing a hole in the duct. John and his crew run for the exit but are stopped by steam nozzles and strike clones, prisoners who have been converted into cybernetic soldiers. Stiggs is killed by a clone when he tries to surrender. John and the men are able to overpower one and steal the gun built into its arm. When the splattergun is sent to their level, it cannot track them and they ride its carriage to the top level.In his offices, Poe secures the room and traps himself, Abraham and Karen inside. When Karen and Abraham try to kill Poe, he overpowers them and kills Abraham. John, D-Day and their cellmate, Nino arrive at Poe's quarters; Poe shows John that Karen has been taken to an operating room where Karen's baby will be removed from her abdomen by Cesarean section and she will not survive the procedure. John forces Poe to take him to Karen, however, ZED sends the splattergun and Poe is destroyed. Zed tells John and his crew that a unit of strike clones are being sent to their location. D-Day tells John to get him to ZED's computer console and is able to successfully disrupt ZED with a computer virus -- moments later, D-Day is killed by a strike clone. The virus is enough to shut down the lights in the surgical lab and delay the doctors long enough for John to find Karen. John, Karen and Gomez escape to the surface where they steal a MenTel truck and drive off, finally arriving in a forested area where Karen goes into labor in an abandoned barn.Suddenly the truck they stole, still controlled by ZED, tries to run them down. Gomez is killed, however, John is able to destroy the truck with the weapon he'd stolen, setting it on fire with the flame thrower. The truck swerves into the barn where Karen had been in labor and explodes. John believes Karen and his child are dead until he hears the child wailing and sees Karen alive; she'd escaped the barn shortly before. John and Karen look at the face of their newborn child.