Cliff Robinson arrived early for work on April 26, 1986, so he decided to go to the break room and grab some breakfast. He wanted to brush his teeth afterward, and that meant a trip to the building's changing room. To return to his office, protocol said he had to scan himself with a radiation detector, because the changing room was in the protected section of Sweden's Forsmark nuclear power plant. That's when the alarm went off. The detector had sniffed out some radioactive dust on his feet. Ooof.
It was a lot of dust -- enough that the plant couldn't just send Cliff over to the showers, but had to order a whole evacuation. Apparently, something had gone horribly wrong. But Cliff figured Forsmark couldn't be the source of the dust, because he hadn't gone to the "controlled area" of the plant, where all the fun stuff happens. He stayed behind as the plant was evacuated, brought a shoe to the lab for further analysis, and found that some of the elements responsible for the radiation didn't even exist in Forsmark. They were created through nuclear reactions of some kind. Had someone secretly set off a nuclear bomb?
The radiation had indeed come from a nuclear plant, just not Forsmark. Based on the wind direction, the dust had to have come from the southeast, all the way over the Baltic Sea. They considered Lithuania at first, but then eyes turned to a plant in Ukraine, almost 1,000 miles away. Once contacted, Moscow was like "Nah, we cool! Please stop asking immediately, or suffer consequences." Sweden said they were going to inform the International Atomic Energy Authority either way, and Moscow reluctantly admitted that, um, yeah, something had happened at Chernobyl.
The Chernobyl plant had just experienced history's worst nuclear disaster, as seen in the recent super-popular HBO miniseries Chernobyl. The show doesn't include anything about Cliff or Forsmark, but it does invent a new scientist in a distant nuclear plant who detects Chernobyl's radiation. HBO put her in Minsk, 250 miles from the plant, because setting the scene all the way in Sweden would have seemed unrealistic, right?