Charlie, an inquisitive teenager uncovers a treasure in the forest. In finding its rightful owner, she restores the memory of a great passion and also her own path.

On a hot summer night in Paris, Lou, 26, is throwing a party at her place. As the the time goes by, she appears to be at a crossroad in her life, slowly realizing she is not as happy and fulfilled personally and career-wise as she thought she was. A chapter will close that night, leaving room for a brand new start.

Commissioner Maigret rushes to the Quai d’Orsay with Lieutenant Janvier. There, they find Mademoiselle Larrieu in a state of shock. That very morning, she discovered the bullet-riddled body of Mr. Berthier-Lagès, a renowned former ambassador whom she had served as a housekeeper for 46 years. While searching the victim's apartment, Maigret and Janvier uncover hundreds of letters. The diplomat had maintained a fifty-year-long love correspondence with a certain Princess of Vuynes, whose husband - by a strange coincidence - had died just a few days earlier. As he confronts the various members of the two families and the suspicious silence of Mademoiselle Larrieu, Maigret finds himself faced with surprise after surprise, watching his certainties crumble - until the solution to the mystery finally hits him in the face at the very last moment...