“Whatever good we did doesn’t matter,” a solemn voice says to open the first trailer for HBO’s miniseries. “What does matter is that, to them, justice was done. See, a just world is a sane world. There was nothing sane about Chernobyl.”

Whoa.

HBO

From that ominous beginning, the trailer shifts to the almost upbeat tone of a Soviet official trying to calm initial fears about the worst nuclear disaster Planet Earth ever has known. “I’m pleased to report that the situation in Chernobyl is stable,” he says reassuringly to an array of concerned faces. “In terms of radiation, I’m told it’s the equivalent of a chest X-ray.”

But the room then gets a dose of reality “No!” insists the man leading USSR’s investigation, slapping his hand on the table. “Chernobyl is on fire!”

That’s the setup for HBO’s five-part mini about the infamous April 1986 accident at the nuke plant in Ukraine, which was hit with a massive explosion that sent radioactive material as far as Scandinavia and Western Europe. Chernobyl stars Jared Harris as Valery Legasov, the ill-fated chief investigator, along with Stellan Skarsgård as Boris Shcherbina, deputy head of the Soviet government and chairman of the commission looking into the accident; and Emily Watson as Ulana Khomyuk, the Soviet nuclear physicist committed to finding out how and why it happened.

The mini kicks off May 6 on HBO.