TV news reporter Kimberly Wells (Fonda) and her cameraman Richard Adams (Douglas) visit the Ventana nuclear power plant outside Los Angeles as part of a series of news reports on energy production. While viewing the control room from an observation room, the plant goes through a reactor SCRAM. Shift supervisor Jack Godell (Lemmon) notices what he believes to be an unusual vibration during the SCRAM. On the control console, a chart recorder indicates that the water level in the reactor core has risen to an abnormally high level. The crew begins opening relief valves in an effort to prevent too much water from damaging the plant, but the chart continues to indicate off-scale high. Minutes later, a crew member notices a gauge on the control panel showing that the water level is dangerously low. Suspecting that the recorder pen may be stuck, Godell taps on the glass cover. He watches, sickened, as the pen trace rapidly drops to show that the water level is now mere inches away from exposing the reactor core, and still falling. The staff scrambles to close the relief valves and restore coolant systems, but for several agonizing minutes, no one knows whether the core is about to undergo a disastrous meltdown. Eventually, backup systems are able to slow and reverse the falling water level, and the reactor is brought under control.
In the observation gallery looking out over the control room, Adams began filming the activity below; when told he was not permitted to film the control room for security reasons, he surreptitiously tucks the camera under his arm and begins filming anyway. Because the glass is soundproof, the visitors can only guess as to what is happening.
When they return to the television station, the station's news director refuses to air the footage, fearing criminal prosecution. Adams, believing that there is more to the story than is indicated in the plant's official statement (which referred to the near-meltdown as an "unexpected transient"), steals the film from the station and shows it to a pair of experts, who are able to fill him in on what actually happened.
Meanwhile, Godell, suspecting there to be more to the strange vibration he felt at the beginning of the SCRAM, does some investigating of his own and uncovers evidence that the plant is unsafe. Specifically, he finds evidence to suggest that another reactor SCRAM at full power could cause the cooling system to be severely damaged. Godell asks the plant foreman to delay restarting the reactor, but he refuses, under pressure from the plant's owners. Godell then contacts Kimberly Wells, asking her to help get his concerns heard. Wells and Adams agree to help get Godell's evidence entered at safety hearings for a new plant being built. Godell asks to remain anonymous, but when the original messenger is run off the road by hit men (presumably hired by the plant's owners), he is forced to appear at the safety hearings himself. On the way there, he is chased by more hit men, and finds safe harbor at the power plant.
When Godell arrives, he finds the plant has been brought up to full power. Now convinced of the evidence, he grabs a gun from the control room's security guard and forces everyone out. Once alone and secured inside the control room, he brings the power down to a safer level. He also tells the plant's managers that if anyone attempts to take control of the reactor from the outside or break in, he'll open valves and flood the containment building with radiation, essentially ruining the plant. He then demands to be interviewed live on television by Wells.
While Wells and Adams set up their equipment, plant technicians find a way to cause a reactor SCRAM. In the middle of the live interview, the SCRAM is started, the camera's cables are physically cut, and a SWAT team forces its way into the control room and shoots Godell dead. Proving Godell's fears true, however, the SCRAM causes significant damage to the plant, as portions of the cooling system physically collapse. The reactor is eventually brought under control by the plant's automatic systems.
Outside the plant, a phalanx of reporters and television crews are awaiting word on the events inside. When the plant spokesman suggests that Godell was "emotionally disturbed" and that he "had been drinking", Kimberly Wells confronts the spokesman in front of the other reporters, and eventually gets one of Godell's co-workers to admit that Godell would not have taken such drastic steps had there not been something to his belief in problems with the plant.
- largely from Wikipedia
