I looked up the Lyell expedition, which gets mentioned on the very first pages of the book. Apparently the fictional and the real expedition don´t have a whole lot in common and I skimmed through the author´s note in the back of the book, which says that the author has made the story of the Lyell expedition up. The real Lyell expedition had its own set of dramatic events and eccentric characters, but nothing to justify a ghost story. So I guess Michelle Paver made the right decision in inventing a fateful expedition.
I really appreciate the gloomy atmosphere of this book. The mountain being shrouded in clouds, the superstitions of the sherpas and the blatant disrespects of the mountaineers, who don´t believe in said superstitions. There is a lot of foreboding going on in this novel.