A rather strong hint when this plot was taking place is shown around 34 minutes, where Maigret has a newspaper "Le Monde" placed on top of what looks like a calendar. You can only see a mirror image of writing through the paper that is turned and it states Octobre 1955.
A very free adaptation of a very early Maigret novel, updating the period of the story by almost a quarter of a century to the mid-50s, adding several references to the Second World War, greatly increasing the role of the provincial police officer Inspector Grandjean to provide a guest part for Kevin McNally and even changing the identity of the chief villain.
Inspector Maigret travels in a Citroen Traction Avant.
Throughout the movie there are several references to the war and the Holocaust, presumably WW2, yet the original novel on which the movie is based was published in 1932 and could not have envisioned them.
(Although they have no screentime together here) Ben Caplan and Dorothy Atkinson both appeared previously on Call the Midwife.