While working for a railway tunnel in the Alps, the geologist Peter Meissner suddenly finds a valley that doesn't exist on any map. On a reconnaissance flight with his hang glider, he falls in the midst of some men who seem to have been isolated from the world for decades. At the beginning, these very religious people are afraid of Meissner and they chase him as if he was the incarnation of Evil. Meissner then tries to solve the mystery through the women of the community. But the religious fanaticism with which the patriarch Z'graggen rules the people is a constant threat. Despite the feelings he develops for a young woman, Sarah, Meissner has to find a way to escape as soon as he discovers the secret of the community.