United Nations troubleshooter Alan Brooks, later joined by journalist Philip Truscott, investigating unusual accidents occurring in the area of a resort hotel on (the fictional) Mount Trollenberg in Switzerland. Brooks suspects these deaths are related to a series of similar incidents that occurred three years earlier in the Andes mountains, which involved an unexplained radioactive mist and odd cloud formation believed by locals to be inhabited.

References:
https://en.wikipedia.org/wiki/The_Trollenberg_Terror