After being congratulated by the KGB for publicly affirming that the Chernobyl explosion was caused by "operator error," Legasov weighs the price of telling the truth at the upcoming criminal trial of Dyatlov, Bryukhanov and Fomin. As proceedings begin in Chernobyl City, Shcherbina, Legasov and Khomyuk lay out the scientific and human explanations as to what went wrong on the night of April 26, even as Shcherbina and Legasov show signs of deteriorating health. The events inside the control room leading up to the explosion are witnessed, and as Legasov's testimony comes to a close, he puts his reputation, and perhaps his life, at risk in hopes of preventing another Chernobyl.