Marie-Chantal travels by train to her cousin's place to spend a winter holiday, when a stranger entrusts her with false jewels that contain a virus powerful enough to destroy all humankind.

Marie Laforêt
as Marie-Chantal

Francisco Rabal
as Paco Castillo

Serge Reggiani
as Ivanov

Charles Denner
as Johnson

Stéphane Audran
as Olga

Akim Tamiroff
as Prof. Lambaré / Dr. Kha

Roger Hanin
as Bruno Kerrien

Antonio Passalia
as Sparafucile

Pierre-François Moro
as Hubert de Ronsac

Robert Burnier
as A Swiss Gentleman