During a night of debauchery in a refined mansion a young student he preferred to go away nauseated while the old lady Mithilde continued to spy on the movements of the other guys. Late at night, she has to find the lifeless body of Raymond Couchet, owner of a renowned pharmaceutical laboratory, lying on his desk in his office. Someone killed him with a pistol and robbed her safe. Inspector Maigret is called to investigate a story that has many dark sides.