Stéphane Blanchon, who teaches at the International College, lives a quiet comfortable life in Geneva. He is married to Christine, a cold, dry-hearted woman, and his sentimental life is reduced to zero. One day, Belle Shermann, an American student and daughter of one of his wife's friends, comes to stay at their villa. The teacher hardly notices her. But his dull uneventful life is turned upside down when Belle is found strangled to death. Blanchon, who was alone with the victim but claims he was sleeping in his room at the time of the crime, is soon suspected of being the murderer...