At the Hoover work camp of the Windsor County Department of Correction, a place where formaldehyde is produced, the warden, whose methods are cruel and outdated, realizes that his career is over. The camp soon will be closed and he has received a letter stating that his attitude is not in alliance with the “new system.” Among the prisoners, who will be dispersed to other institutions, there is a faction that has become addicted to the fumes of formaldehyde. Encouraged by their ringleader, Braddock, these men frequently indulge in an orgy of breathing fumes and dousing themselves with the liquid, while they take turns standing guard. The chemical has softened their minds, which makes it easier for the vicious Braddock, who is engineering a prison breakout, to control them. That afternoon, Carol Johnson, a waitress living in a nearby trailer camp, approaches the prison gate to see her husband Paul, who is serving time. McGee and Sgt. Jablonsky, two compassionate guards, open the gate to allow Paul to step out for a brief time to speak with her in private. As they converse, the other prisoners watch intently from a distance. That evening in the barracks, Braddock invites Paul to escape with them, but when Paul expresses concern about an attack on McGee that is part of the escape plan, Braddock abruptly stabs him, leaving him to bleed. Later, Braddock and his followers kill McGee, steal weapons, and make a successful escape. However, when one of them trips, he accidentally fires the rifle he is carrying, which alerts the prison employees. The warden, accompanied by guards, searches the camp, during which the seriously injured Paul is found and treated by the prison physician, Dr. Saunders. The warden and his men then pursue the escapees, who, during an exchange of gunfire, are killed. The warden orders the guards to load the bodies onto a prison truck then bury them in an unmarked grave. Not content, the warden next rounds up the remaining prisoners, even though they did not attempt to escape. As punishment for not reporting Braddock’s plans, and despite the protests of Saunders and a prisoner who points out that the treatment is illegal, the warden orders that they be chained together in a standing position and left outdoors for three days. Meanwhile, as guards dig the graves, barrels of formaldehyde that have been riddled by gunfire leak onto the corpses and into the graves. The corpses then come alive, some pushing their way out of the dirt, and kill the gravediggers. Taking shovels, an axe and other weapons, the zombies proceed toward camp, while, in emotionless voices, they chant, “We will destroy the living!” In a nearby trailer camp, Carol is visited by Saunders, who tells her about Paul’s injuries. To calm her, Saunders gives her an injection of sedative and offers his assurance that Paul will recuperate. Before leaving, Saunders speaks with the Flemings, the kindly neighbors who have been watching over Carol. After the doctor leaves, Carol, who is barely able to stay awake, hears Mrs. Fleming cry out, and through the window sees her neighbor murdered by the strike of an axe. Carol struggles to the driver’s seat at the front of her mobile home, as her screaming and crying lures several of the zombies toward her vehicle. After barely escaping from them, Carol drives to the camp gate. Jablonsky allows the hysterical Carol to be brought inside and taken to the warden’s office. As a guard locks the gate behind her, he thinks he sees an axe-wielding Braddock, as well as the other dead men in the fog. Soon after, the camp’s power goes out and the telephone line is dead. A guard sent to check the power lines is later found killed, hacked by an axe. The warden then issues ammunition to his men and arranges to have the generator power a searchlight, but he refuses to believe guards who claim they see the dead prisoners walking in the distance. As the warden and his men search the entire camp, they discover that the motors of the prison vehicles have been destroyed. The warden decides to send the prison’s youngest and fastest athlete, who is one of the chained men, by foot to alert the sheriff in the town several miles away. As the warden and his guards approach the chained men, several zombies are about to attack them. In the ensuing struggle, the warden realizes that they are, indeed, the dead prisoners but they can be incapacitated permanently by shooting them in the chest at close range. The chained prisoners then are released and sent to the generator plant, which is the strongest building at the camp. However, while they leave, a zombie takes them by surprise and kills the warden, which leaves Jablonsky in charge. As the remaining zombies refuel with formaldehyde fumes, the injured Paul is reunited with Carol in the warden’s office. A zombie attacks the office window, but the beam of a search light causes it to decompose. Jablonsky orders that the beam be pointed toward his group, as he leads Carol, Paul, Saunders and others slowly toward the generator plant. All is quiet as they walk toward the building, watched by the zombies. When the light weakens, the zombies draw nearer and attempt to attack, causing Carol to be left momentarily vulnerable, but the creatures do not touch her. After the group is safely inside the building, Jablonsky expresses surprise that the zombies did not harm Carol. Paul says that Braddock’s men often taunted him, by telling him how much they wanted to touch her. Realizing that help may not arrive before the zombies are able to break into the building, Jablonsky asks for Carol’s assistance with a plan. Just then, the zombies, who have taken time to refuel, approach the building and call out, “Show us the girl. Send her out.” Walking toward the beam of light Carol proceeds, armed with a shotgun. When she hesitates to shoot, Jablonsky and other guards step out from behind the door and fire at the remaining zombies at close range, permanently putting an end to their ordeal. As the guards check to assure themselves that safety has been secured, Carol cries on Paul’s shoulder.