In a dusty back corner of his new office at Global Dynamics, Fargo uncovers a complex control console and, curious, activates it. Within moments, missile silos sprout like hideous flowers throughout the town, and an ominous countdown begins. Fargo has awakened a forgotten weapon of the Cold War - and in 24 hours, it's going to fire.
As the countdown clock ticks down, Jack and Zoe meet with the dignified old woman. She confesses that she and Thatcher once hoped to be married, but when he lost the coveted Nobel Prize in 1962, he suffered a complete mental break. Ever since, he's been trapped in his own mind, reliving his greatest disappointment over and over. To stop the coming apocalypse, Jack must first revisit the long-ago day that Irvin Thatcher's own world fell apart - and he'll need the whole town's help to do it.
Jack, Henry, Allison and Stark converge in Fargo's office to investigate. The weapon is an ionosphere particle beam - a "death ray," in Jack's apt but unscientific jargon - that bounces a beam of irradiated uranium isotopes back to Earth from a mirror on the surface of the moon. Henry can't shut the weapon off, and any attempt to destroy it will cause it to activate immediately. There's no way to know whether its target will be Moscow, Eureka, or someplace else. But the resulting destruction will be massive - enough to trigger World War III.
The weapon was invented by Dr. Irvin Thatcher, a once-brilliant Cold War scientist who now lives in Eureka's posh retirement home. By chance, that's exactly where Zoe is enduring community service for pulling the school's fire alarm. She introduces Jack to Eugenia, a witty but kind resident of the home. Jack finds Thatcher and whisks the aging scientist back to Global Dynamics, where Henry interprets his seemingly senile suggestions and succeeds in accessing the machine's innards. Then, however, Thatcher subsides into complete dementia, unable to tell them anything more about his greatest invention.
Henry and Stark's subsequent tinkering with the machine accidentally advances the countdown from twenty hours to seven. Now they need Thatcher's help more than ever, so Jack risks a dangerous experiment. Using Stark's latest project - an untested machine that enables one person to probe the consciousness of another - Jack takes a disorienting tour of the scientist's memories. While he can't gather any straightforward information about the weapon, he does learn that Thatcher is in love with Eugenia.