Did Doctor Maupin poison Madame Goron? In any case, this is what his niece suspects, who calls on the O Agency. When the aunt dies, everything seems to overwhelm the doctor, who nevertheless has an indisputable alibi: he was being watched by the agency! How could he have transported the corpse? Unless the Agency was deliberately put on the wrong track ...

Much to the chagrin of the official police, members of the O Agency are crossing the legal line widely - and repeatedly - to prevent a saxophonist from being charged with murder. They manage - but with difficulty - to establish proof of the plot aimed at compromising the musician.

José is a saxophonist in a nightclub run by a manager nicknamed "The Banker". Kikou, the mistress of "The Banker" also works in this nightclub as a stripper and also prostitutes herself with large clients. José is attracted to Kikou and she is not insensitive to the young man. Having surprised them, "The Banker" decides to take revenge ...

Shot by a gun, a client comes to die in the offices of the O Agency. He is a comfortable bourgeois from Saint Etienne who was due to marry his son the next day. The only clues: a metro ticket, and in his pocket a large revolver that was used a short time ago. But why did he regularly receive boxes of watercolors in the mail when he wasn't painting? When his last words, more or less intelligible, are finally understood, the evidence stands out.

A leak occurred at the O Agency. What should at all costs remain secret fell on the ears of thugs who took advantage of it to exercise blackmail, and also to make the police believe that the Agency itself, even is wet in the combination. Dispelling police suspicion is far from easy. Until a few acoustic properties are discovered.

The painter Tigrane Alban murdered Evjen because he had dishonored his daughter Dalté. The members of the O Agency are the only ones to know about it, but soon the painter is blackmailed. So there is one of the members of the O Agency who is responsible for the leaks. Miss Berthe feels that everything accuses her ...