The Trollenberg Terror

Two sisters, Anne (Munro) and Sarah Pilgrim (Jayne), a London mind-reading act, are travelling by train to Geneva when Anne faints as the train passes the mountain. Despite many climbing accidents, no bodies are ever found; an always-stationary radioactive cloud is regularly observed on Trollenberg's south face. Similar incidents took place in the Andes three years earlier, before a similar radioactive cloud vanished without a trace. Local rumours circulated that something was living in the mist.