April 26, 1986, Ukrainian SSR. Plant workers and firefighters put their lives on the line to control a catastrophic 1986 explosion at a Soviet nuclear power plant.

With untold millions at risk after the Chernobyl explosion, nuclear physicist Ulana Khomyuk makes a desperate attempt to reach Valery Legasov, a leading Soviet nuclear physicist, and warn him about the threat of second explosion that could devastate the continent.