In the bleak Russian winter of 1959, nine experienced hikers led by Igor Dyatlov set out on an expedition. None of them made it back alive.

When their campsite was finally discovered, it told a chilling story: their tent was slashed open, bodies scattered across the snow. The hikers' injuries were as baffling as they were gruesome. One had had his head stoved in. Bits of bone had been driven into his brain. Others were missing their eyes and their tongues.

Had the hikers angered the local Mansi tribespeople? Had they witnessed a secret military experiment? Or had something even more strange and sinister unfolded on Dead Mountain?

For a full list of sources, see the show notes at timharford.com.