When construction of a new prison is behind schedule, prison overcrowding forces the state of Wyoming to reopen Wyoming State Penitentiary in Rawlins, which has been closed since 1968. Ethan Sharpe is appointed to be the warden. Three hundred prisoners are transferred into the aging facility and put to work cleaning it up. When two inmates, Rabbitt and Hershey, try to escape, Sharpe puts them in solitary confinement and punishes everyone else by canceling all mail and visitation privileges. Sharpe who worked at the old prison as a guard and witnessed the 1964 electrocution of prisoner Charles Forsythe, still has nightmares about it. He also has the gold chain and crucifix that Forsythe wore around his neck. One day, Sharpe sends several inmates, including Burke and his cellmate, Joe “Lasagna” Lazano, into the basement to break through a wall that conceals the execution chamber. As they do so, various machines throughout the prison self-activate and explode. Lightning bolts emanate from the execution chamber and spread through the penitentiary. One prisoner’s hands are burned, and he reports that he shook hands with a spirit. As water covers the floor in the solitary confinement cells, Hershey screams that the ground is on fire. Burke rushes in and saves Rabbitt, but Hershey’s body is burnt to a crisp. Despite Burke’s heroism, Warden Sharpe warns it will make no difference to the parole board. Put back in a regular cell, reports Rabbitt devises an escape plan, but Burke wants no part of it. Sharpe goes into the old execution chamber and places Charles Forsythe’s gold chain and cross on the electric chair. An instant later, the prison’s power shuts down. Sharpe orders a prisoner count, but Rabbitt makes his escape just before they go into lockdown. As he sneaks through the bowels of the prison, Rabbitt sees metal tubing, pipes, and ropes move on their own, seemingly controlled by supernatural forces, and the pipes kill him. The next day, when Rabbitt’s body falls through the ceiling into the cafeteria, prison board member Katherine Walker demands an investigation of the two inmate deaths. Sharpe orders guards to collect all the mattresses from cells and place them in the courtyard. He douses them with gasoline and sets them on fire, declaring the prisoners no longer have cells, only cages. Believing Rabbitt was murdered, he demands the killer confess, but no one responds. Sharpe orders a guard to do a body search of each prisoner, then makes the convicts stand in the courtyard in their underwear through the night. The next morning, when an older prisoner, Burton Cresus, collapses from exhaustion, the guards harass him. Burke is blamed for the incident and placed in solitary confinement. Meanwhile, a guard is attacked by a coil of barbed wire that strangles him. When another guard comes into the break room, he, too, is attacked by the wire. Afterward, the coil pushes the first dead guard’s body through the ceiling into Sharpe’s office. Sharpe puts the prison on lockdown, but just as the prisoners return to their cells, the power goes out and guards cannot lock the cells. The prisoners riot, but guards get them into their cells and manually lock the cell doors. Meanwhile, the electrical devices in Katherine Walker’s motel room, including her computer, turn themselves on. Her computer screen repeatedly flashes “1964 . . . The Prison Dies Tonight!” She goes to the local newspaper and learns that Charles Forsythe’s 1964 execution was the last carried out there. Forsythe’s picture looks like Burke. In a cell, a prisoner cuts his chest repeatedly with a shard of glass while repeating an incantation to summon the “creature of darkness.” Suddenly, a hole appears in the wall and multiple bolts of lightning hit him and other prisoners. The cell doors explode open and the electricity goes out in the entire prison. As the prisoners try to escape, Sharpe goes to the infirmary and chastises Cresus, who tells him that Charles Forsythe’s spirit is exacting revenge. Cresus, who was an inmate at the prison when Sharpe was a guard, witnessed him killing a prisoner, then helped him frame Forsythe for the murder. Their testimony sent Forsythe to the electric chair. In the years since, Sharpe has arranged for Cresus to get easy prison assignments. Meanwhile, Burke escapes solitary confinement, goes to the infirmary, and takes Sharpe hostage. As prisoners dash across the courtyard to freedom, machine guns on the guard tower begin firing. Arriving in her car, Katherine dodges gunfire. Cresus and Burke convince her to drive them and their prisoner, Sharpe, out of the prison, but the prison gate close before they can escape. Burke climbs the prison wall to open the gate from the guard tower, then makes his way down the other side of the wall. As Katherine drives through the gate, Cresus dies. When she stops for Burke, Sharpe steals the car and drives away, but a bolt of lightning hits the road in front of him. Sharpe sees the image of Forsythe being electrocuted. The car explodes, killing him, but Burke and Katherine survive.