Stanislas Oscar Seminario, aka SOS, is a young explorer, just back from Africa, visiting old friends: the Pescara’s. But the father keeps receiving anonymous letters. And soon a mysterious murder…

To try solving the strange disappearances of 11 young Parisian women, the police obtain the services of Adrienne Charpentier, friend of the latest missing person.

After committing a murder, a man locks himself in his apartment and recollects the events the led him to the killing.