As the USSR collapses, an investigation uncovers the cause of the accident and scale of the Soviet cover up. Today, Chernobyl's toxic legacy persists as the nuclear exclusion zone becomes a war zone, raising fears of another disaster.

In the weeks following the meltdown, workers battle lethal radiation to clear debris and construct a protective tomb around the destroyed reactor. Amid speculation, Soviet scientists reveal what they can about the cause of the catastrophe.

The day after the incident, helicopter crews brave deadly radioactive smoke to extinguish the fire raging in the reactor core. As 50,000 locals evacuate, Soviet authorities try to conceal the scale and human cost of the accident.

On April 26, 1986, a massive explosion rips through a reactor during a safety test at a power plant in Ukraine, triggering the worst nuclear accident in history. Within 24 hours, a lethal radioactive cloud starts to circle the globe.