They were students at the Ural Polytechnic Institute in 1959 and during their winter break they planned this hike so they could qualify for a Level 3 hiker's certificate. They were experienced and fit (except for the one man who had to turn back). What, then, made them leave their tent in the middle of the night, without their overclothes and boots?
Theories ran the gamut from escaped gulag prisoners to wild animals to aliens. The author, Donnie Eichar, decided to solve this real-life mystery. He got all the records, pictures, and logs he could find. He also went to Russia, met the lone survivor, and followed in their footsteps.
The answer was surprising and rooted in advanced physics. The work to solve the mystery was very interesting.