At the Stonehaven Maximum Security Prison in Alaska, inmate Oscar “Manny” Manheim, who is serving a life sentence, wins a civil rights case against the prison for keeping him welded inside a cell for three years. After hearing the report on the television, the inmates go wild and riot in support of Manny. Warden Ranken defends his actions on camera noting that Manny is an animal who has broken out of prison twice before. Ranken returns to the prison and releases Manny from his cell and allows him to walk the yard, where he is reunited with his prisoner friend, Jonah. During a prison boxing match, Manny is attacked and stabbed through the hand by a fellow inmate. Ranken watches from a floor above as the men fight. Jonah murders Manny’s attacker and is severely beaten by the guards. As Manny and Jonah recover from their injuries in the prison hospital, Manny tells him he is going to break out again, but Jonah refuses to join him. However, an inmate named Buck helps Manny escape in a laundry bin, and begs to come along. Manny reluctantly agrees. They grease themselves up and escape through the sewage pipes. After falling into a frigid river, they make their way across the frozen tundra, eventually arriving at a train yard. They sneak aboard a train, but as it leaves the yard, engineer Al Turner has a heart attack. The train speeds along unmanned, and the yard workers call Central dispatch to report the four-car runaway. Meanwhile, Warden Ranken searches for Manny and Buck by helicopter. Buck looks up to Manny, and compliments him on his previous bank-robbing crimes. Buck exclaims he is going to party now that he is free, but Manny instructs him to find a menial job and be thankful, insisting that collecting a weekly paycheck is “like gold.” The runaway train picks up speed and Manny suspects something is wrong. The engineers at the Central dispatch office frantically warn oncoming trains to switch tracks. When a locomotive changes tracks too late, the runaway smashes into its caboose. Manny and Buck are thrown by the impact, but their train fails to slow down. Manny surmises there is no engineer onboard, and he and Buck make their way to the front of the train. Elsewhere, Ranken gets word that prison clothes were found at the switchyard. The Central office dispatchers worry that the fast-moving locomotive will destroy a bridge that requires a slow speed to cross it. Believing the train is empty, superintendent Eddie MacDonald sends word to adjust the tracks to cause a derailment. When the signal maintainer reports hearing the train whistle, the dispatchers cancel the derailment realizing someone is onboard. Meanwhile, Manny and Buck are surprised to hear the whistle. When they see a worker in a hard hat approaching their train car from outside, they prepare to fight. As the worker enters, Manny and Buck throw the person to the ground, surprised to see it is a female. The woman, Sara, claims responsibility for blowing the whistle and tells them she works on the train but had fallen asleep and was awakened when they hit the caboose of the other train. They need to cut the fuel switch in the lead engine to stop the train, but she reports that the door to the front car is jammed. Warden Ranken arrives at the dispatch office to monitor the runaway train, suspecting that Manny and Buck are on board. Buck reveals that they have escaped from Stonehaven Prison. Realizing that police will be present when the train is finally stopped, Manny decides to jump from the speeding locomotive, ignoring Sara’s warnings that he will break every bone in his body from the impact. Before Manny and Buck jump, Sara thinks of a way to slow the train down by disconnecting the bus-line cables, and the trio work on the line outside the train. The dispatchers learn that Sara is on board and note the train is slowing down. However, they worry it is still too fast to cross the upcoming wooden bridge. Sara falls between the train cars, and Manny rescues her. Workmen wait near the bridge, anticipating disaster, but the train makes it safely across. A worker sees the threesome onboard, and reports to the Central office. Dispatchers see another train approaching miles down the track, but worry that if they switch tracks it will crash into a chemical plant. Ranken threatens lead dispatcher, Frank Barstow, to direct him to the train, and boards a helicopter to find it. Meanwhile, Manny and Buck try to break down the engine car door. Buck volunteers to make the treacherous leap across a wide expanse to the front engine car. However, when Buck gives up and returns, Manny beats him, calling him a coward. Buck agrees to try again, but Sara pleads with him not to, and calls Manny an animal. Manny throws Sara across the train car and her head smashes a window. He resumes beating Buck and pulls a knife on him. Buck threatens to kill Manny with a wrench, and Sara bites Manny’s injured hand. As Manny prepares to stab Sara, Buck hits him with the wrench. Sara screams for Buck to kill Manny, but Manny drops his knife in surrender. Buck laments that he thought they were friends and had considered Manny a hero. In an attempt to save more lives, the dispatchers plan to derail the runaway train, even though the trio will be killed. Meanwhile, Ranken lowers a rescue man from the helicopter. When the man falls and dies, Manny mocks Ranken. Ranken descends the ladder himself, but the train goes through several tunnels and the warden cannot get close enough. Sara realizes the engineers have switched their track and they are doomed to crash. She asks Buck to hold her. Refusing to die, Manny makes the perilous leap to the engine car but falls between cars and mangles his hand. He drags himself along and enters the engine. Ranken lands onboard with a gun drawn, and follows Manny inside. Manny beats him with a fire extinguisher and handcuffs the warden to the train. Although Ranken warns they will crash in five minutes, Manny refuses to push the emergency fuel shut-off. However, he unlatches the other train cars from the engine to save Buck and Sara. Buck screams for Manny to save himself, but Manny ignores him. As Buck and Sara’s car comes to a stop, Manny defiantly stands atop the engine as it speeds to his death.