I recently read the first two of English author Adrian Magson's Police series set in the 1960's in the Amiens region of France and thoroughly enjoyed them.
I suggest that they would interest readers of Donna Leon, Louise Penny, Martin Walker and Michael Dibdin, even though those books are set in the present times.
The main character, Inspector Rocco, isn't philosophical in nature as are the main characters in Leon and Penny's works, but the overall feel and style of all the mentioned authors books are not too dissimilar.
The 1960's was an interesting period in France for many reasons, but particularly in this context because Amiens was one of the regions still recovering emotionally, mentally, physically and environmentally from both the First and Second World Wars.
The synopsis of book 1,
Death on the Marais, as follows
The synopsis of book 2,
Death on the Rive Nord, as follows: