Survivors recount the terrifying first 24-hours of the worst nuclear accident in history. After a reactor explodes during a safety test at a power plant in Ukraine, firefighters rush to the scene, unaware of the lethal levels of radiation. Soviet authorities try to cover up the disaster as a cloud of radiation begins to circle the world.

Two days after the explosion, the world wakes up to a terrifying global disaster. At the power plant, helicopter pilots try to put out a fire in the reactor core, braving plumes of highly radioactive smoke. Soviet authorities eventually begin to evacuate 50,000 people from the local area, while still trying to conceal the scale of the accident.

Workers begin to clean-up the deadly radioactive fallout from the explosion. After troops establish an exclusion zone, Gorbachev orders the construction of a vast concrete sarcophagus to cover the destroyed nuclear reactor. In Vienna the world finally hears the Soviet explanation of what went wrong - but are they telling the truth?

14 months after the disaster, plant operators face a Soviet show trial. At the reactor, scientists hunt for the deadly remains of the radioactive fuel. As the USSR crumbles, an independent investigation reveals the true cause of the accident, and the full scale of the cover up. 40 years later, the nuclear exclusion zone turns into a war zone.