The Dyatlov Pass Incident is one of those weird fortean moments in history. In 1959, nine young ski-hikers died in the frozen wilderness of the north Ural mountains. They were all experienced in the outdoors, and their bodies were found hundreds of meters from their tent, bootless, without their outer layers. The tent had been slashed from the inside, but was mostly intact. An investigation was inconclusive, an "outside compelling force" had caused the deaths. Into the vacuum flooded speculation: natural phenomenon like wind or avalanche didn't match the evidence at the site. Another group could have been responsible, either local Mani hunters or escape convicts, but there were no humans within 50 km of the place where the hikers died. Things got weirder: super-weapon tests, military experiments, UFOs and yetis.

Eichar is an American documentary film-maker who became fascinating by the incident, and out of pocket, funded a expedition back to where they died. In this book, he reconstruct the last journey of the Dyatlov Pass group, the innocent camaraderie of Soviet tourists in 1959 (in the USSR, the word is more like adventurer than fanny packs and buses). Eichar does a decent job reconstructing this, but I can't shake the feeling that he's not the right person. While he has a ear for narrative, and a rigorous skepticism, he doesn't speak Russian and he's not an outdoorsman, and I feel like there are dimensions missing.

Eichar does have an explanation, and it's not aliens. An atmospheric phenomenon called Kármán vortex street sent snow devils whirling off a nearby peak. The vortexes thrummed in infrasound, ultralow vibrations associated with psychological unease, and even extreme distress. Their nerves flaring for no perceptible reason, the Dyatlov group broke under the strain and ran into the night, where they met their deaths from cold and falling.

Ultimately, we'll never know what really happened, but Eichar makes a solid guess.