 Emile Ducrau is assaulted and Maigret is in charge of the investigation. Emile Ducrau is a self-made man and now he is a rich ship-owner. The inquire seems to end when Ducrau s son kills himself leaving a letter in which he declare himself guilty of his father s assault. Maigret, however, is not convinced and keeps on the investigation, a psychological investigation, and Maigret will find out the reality of facts and sentiments, concealed by the appearances.