Veteran Chamonix mountain guide Michel Servoz (Pierre Rousseau) and the young aspiring guide Patrick Falavier (Jeane-Pierre Marry) attempt to climb the west face of the Dru in the Mont-Blanc massif. When they are gone for five days, the captain of the gendarmerie Morteau (Jean Valmont) is worried, but he can not undertake research for a rescue without the permission of the family.
Mary Servoz (Jeanne Allard) wants to respect the wish of her husband to keep the race secret. His daughter Catherine (Joëlle Fossier), engaged to Patrick, does not share this opinion. For her the waiting has been long enough. A journalist reveals that Michel tries to climb the west face of the Dru.
After being rescued Michel recounts the circumstances in which Patrick was killed, struck by lightning. A month later, Michel resumes his activities as a guide. During his first expedition the client reveals his true identity: he is the brother of the deceased Patrick and he wants to know what realy happened high up in the mountain. Again the expedition goes wrong: Michel must sacrifice his life to save that of Philippe Falavier (Georges Claisse).