A government research facility goes through emergency evacuation, but it is a ruse engineered by its boss, the aging Dr Elijah Cooper, and his master-computer ALEX 7000 to get rid of all the personnel. He then makes a worldwide broadcast on television via Athena 18 communications satellite saying he is the inventor of the Cobalt Bomb, the deadliest nuclear bomb ever invented, and he gives a live demonstration. Afterwards he says the demonstration is small compared to what will happen if anyone detonates a nuclear bomb. This will activate his Doomsday Device, which will render the planet lifeless. For the benefit of doubters, he wants the UN to deliver four eminent scientists – Rudy, Dr. Victor Evtuhov (USSR), Dr. Toshiro Kurosawa (Japan) and Dr Marguerite Perry (France) – to confirm he has such a device. He also warns that if they take any military action against him, the device will be activated immediately.
Jaime and Oscar are among those who have watched the broadcast. Reactions worldwide are varied, and Oscar is among those asking questions about Cooper's mental state. The UN agrees that Oscar will be in charge of the operation, but Oscar is not finding the Middle East delegate Mr Satari very cooperative. Rudy and two of the scientists Cooper asked for have arrived, but Jaime will pose as Perri.
Rudy and Jaime arrive at the complex and Jaime decides to go snooping. She finds the operations room, but is surprised by Cooper. He is a bit dubious about her and starts asking questions about her research. She uses the intercom to alert Rudy that she needs some advice about nuclear physics, and he dictates advice for her to hear bionically. Then the other two scientists arrive.
Cooper describes his Doomsday Device to the scientists and then switches on the screen to show his vault, where he says the Doomsday Device is stored, and is impenetrable and failsafe. Rudy asks Cooper why he is doing it, as he has always been known as a man of peace. Cooper (who exhibits warning signs of ill health from old age) says it is to blackmail the world into world peace, as the only thing that can activate it is the detonation of a nuclear bomb anywhere in the world. Its activation will occur six hours after the detonation. When the scientists protest, Cooper turns all control of the complex and the Doomsday Device to ALEX, so he no longer has any control over the matter. He then dismisses the scientists.
The UN agrees not to activate any nuclear devices for the time being until they have a clearer analysis of the situation. But Satari phones to say that his country does not believe there is any such device and have dismissed it as a superpower plot against the nuclear expansion of Third World countries. They are going to perform an atmospheric nuclear bomb test in five hours, and there is little Oscar can do to stop them.
A reconnaissance helicopter is shot down by ALEX and fortifications are too strong for a military attack. Jaime volunteers to go back in to stop ALEX before the detonation occurs. On the way she finds Evtuhov, who is really a Soviet agent, Dimitri. Like Jaime, he posed as one of the scientists to infiltrate Cooper and he is also trying to stop ALEX. So they team up. Jaime takes a moment to inform Oscar about Dimitri, who advises her to take him along, but be careful to hide her bionics from Soviets. But time is soon against them, so Jaime is forced to reveal her bionics to Dimitri so they can speed up. Dimitri says his country had experimented with bionics on humans too, but had failed. And now he knows about the US success, his position as a Soviet agent is compromised.
While crossing a minefield, one of ALEX's laser guns triggers a mine and Dimitri is injured. Jaime goes on to the complex alone, but her entry alerts ALEX. Jaime tries to damage the computer, but ALEX says that it will have no effect.
Jaime finds Cooper, who is now dying. He now realizes she is not the French scientist, but just starts talking about how one never appreciates life more than when looking at death. Jaime tells Cooper that one country is about to activate a nuclear bomb and urges him to tell her how to stop ALEX. Cooper is saddened at the news but says there is no reversal. He then dies.
The nuclear bomb goes off. Jaime gets the alert that the Doomsday Device has been activated and the countdown for the six hours begins.
Oscar had rigged the Athena 18 satellite so that only he and the world leaders would see any further messages from Cooper, not the whole world. So only they see the pre-recorded broadcast from Cooper that the Doomsday Device has been activated and will detonate in six hours.
Jaime tells ALEX she is going to get to the complex where the Doomsday Device is stored. It will be a duel between her and ALEX. Alex says it is foolish and she will only die in the attempt. But he accepts the challenge, and warns Jaime that he is programmed to show no mercy.