Commissioner Maigret is urgently called to the Quai d’Orsay (Ministry of Foreign Affairs) after the murder of Monsieur Berthier-Lagès, a renowned former ambassador. He quickly discovers that Berthier-Lagès had been carrying on a fifty-year-long love correspondence with Princess de Vuynes, whose husband, in a curious twist of fate, has just died. As Maigret faces the members of both families and the suspicious silence of the diplomat's maid, he goes from one revelation to another...