As mysteries go, the Dyatlov Pass Incident is a doozy. More than 60 years after it happened, people are still puzzling over it, positing theories for it, and obsessing about it.

One man does all of this in the Russian drama Dead Mountain (Pereval Dyatlova). He is Oleg Kostin (Pyotr Fyodorov, Sputnik), a KGB major who conducts a confidential investigation into the deaths of nine people who were on a ski hike in the Ural Mountains in early 1959. What led to their demise has come to be called the Dyatlov Pass Incident, named after the leader of the ill-fated group.

The series opens on February 27, 1959, 35 days after the ten-person group of experienced ski hikers set off on their trip. Oleg has been sent by Moscow to the Sverdlovsk Region to find out what happened to them and if they were victims of foul play. He is there in an unofficial official capacity, meaning nothing about him — his name, his face, his voice, his anything — is to appear in any reports or records about the case. However, he’s still the person in power. As Oleg informs Vasily Tempalov (Aleksey Kirsanov, Demons), the prosecutor in Ivdel who’s temporarily leading the case, “I’m not here, yet I’m in charge.”

When Oleg arrives in Ivdel, he learns that the bodies of four of the hikers have been found, as has their tent. But how curious: These hikers were only wearing their sleepwear, not coats, when they died in the snow in sub-zero temperatures. And their tent had been cut open from the inside. So who or what were they trying to escape from?

Sverdlovsk Regional Medical Examiner Ekaterina “Katya” Shumanova (Mariya Lugovaya, Better than Us) is assigned to assist Oleg. She has questions about him and the case, but before she gets answers, she must sign the non-disclosure agreement that he puts in front of her. Her role on his investigation is to perform the autopsies. Similar to Oleg, Katya will be invisible in the the case files, but unlike him, she has no power on the case. The head medical examiner will sign the official autopsy paperwork. Unaware of the existing connection she has to Oleg (while being keenly aware of her fondness for him), Katya’s initial assignment is to autopsy the four bodies that have been found so far on the mountain — what the indigenous Mansi people call Kholat Syakhl. Dead Mountain.

The second episode takes the audience back to January 1959. Igor Dyatlov (Ivan Mulin, Crystal Swan), a student at Ural Polytechnic Institute, receives approval for the difficult route to Otorten and picks up the permit for the group trek. At the same time he learns that 30-something ski instructor Sasha Zolotaryov (Egor Beroev, Best Frenemies) is joining the group, and there’s nothing Igor can do about it. So the group of ten, consisting of eight men and two women, set off for their adventure on January 23, 1959.

By the end of January 1959, one member of the group has turned back, leaving his friends to continue onward and upward toward their final destination of Otorten. By the first week of March 1959, four of their bodies still haven’t been found, but postponing the search until the snow begins to thaw isn’t an option. So the searchers keep looking, and April comes and goes. It isn’t until the first week of May that the final four bodies are located. Katya’s autopsies point to hypothermia and fatal injuries brought on by severe traumas to the body as the causes of death for the nine hikers. And Oleg makes a determination about the events that led to their individual and collective demise.