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…

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

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.