Season synopsis
Contains spoilers for this season and earlier seasons.
The story opens with Valery Legasov’s suicide, then returns to the night Reactor 4 explodes. Deputy chief engineer Anatoly Dyatlov rejects warnings that the reactor core is gone, while firefighters enter the burning plant unaware of the danger. Legasov is summoned to advise a government committee and travels with party official Boris Shcherbina. Scattered graphite confirms the core has ruptured. Shcherbina’s disbelief gives way to action, including ordering nearby Pripyat evacuated as Soviet authorities try to contain the fire and limit radiation.
Ulana Khomyuk, a fictional composite of several scientists, detects radiation in Belarus and warns Legasov that the fire could trigger a second explosion. She investigates at a hospital, questioning surviving operators about the failed safety test and pressing Dyatlov for an explanation. Legasov and Shcherbina organize more containment work: three workers enter flooded basement passages to open valves, while miners dig beneath the reactor to protect groundwater. At Moscow’s Hospital No. 6, Lyudmilla Ignatenko stays near her gravely ill firefighter husband Vasily, tying one family’s ordeal to the investigation.
Months into the cleanup, liquidators clear abandoned villages and kill contaminated pets. Machines cannot handle the most radioactive roof debris, so men are sent to clear it by hand. In the finale, Legasov explains the delayed safety test and the RBMK control-rod flaw, admitting that his earlier Vienna testimony concealed it. The episode uses a dramatized courtroom sequence, with Khomyuk presenting the investigation evidence. Soviet officials suppress Legasov’s testimony and sentence the plant managers. Stripped of influence, he records the truth on tapes before taking his life.