M. Emile Parendon, a business attorney, receives a letter which may or may not be a threat. As a favor, Commissaire Jules Maigret looks into the affair, though there's no real crime -- yet. Suspects include Mme. Parendon, one son, one daughter, three employees, and three servants. (Each of these gets a one-line character description courtesy of the butler in an amusing exchange.) With the able assistance of his nephew Paul, Maigret has to uncover what's going on before someone gets hurt -- especially after he gets letters himself.
As one can tell from the title, the Parendons are indeed rich, and most of the action takes place in their strikingly opulent home, which also holds M. Parendon's office. The story unfolds quietly enough, as is the case with the other Maigret films I've seen. There's plenty here to hold one's attention. As an aside, Celia Granier-Deferre (playing Bambi Parendon) is the daughter of director Denys Granier-Deferre, who is the son of teleplay adapter Pierre Granier-Deferre. All in the family!