The nuclear power plant near Chernobyl is due for routine tests. Foreman Anatoli Diatlov is supervising tests on reactor number 4. Confident in his equipment, Diatlov decides, against the advice of his engineers, to push the reactor tests to the limit and disables several security measures. When the team notices the reactor is overheating, they trigger the alarms. But it’s too late, and reactor number 4 goes into irreversible meltdown and explodes, sending dozens of tons of radioactive steam into the atmosphere. Part of the "Butterfly Effect" series.