It's German-occupied France during the Second World
War. Two honest detectives, one from each side of that
war, fight common crime in an age of officially
sanctioned crime on a horrendous scale. Gangsters
have been let out of jail and put to work by the
Gestapo and SS; collaborators welcome the Occupier
and line their pockets; ordinary citizens struggle to
survive; inflation hits 165% while wages are frozen at 1939 levels; but most of all, German
servicemen come on leave to Paris, ‘our friends' to some, ‘the Green Beans' to others, the ‘Schlocks, the Boche'.
Paris, unlike all other cities and towns in war-torn Europe, is an open city, a showcase Hitler uses to let his boys know how good things can be under Nazi rule. French Gestapo are everywhere and definitely don't like these two detectives since St-Cyr put many of them away before the war, but Kohler is all too ready to tell them this and is fast becoming a citizen of the world under Louis' influence and also has no use for the Occupier, even to ridiculing Nazi invincibility. Hated and reviled by the Occupier and often by the Occupied, the two constantly tread a minefield.
Paris is home territory but as the only two honest cops around, they are sent throughout the country, so we see aspects of the Occupation from different perspectives, yet everywhere there is the nightly ink of the blackout and the nail-down of the curfew. Muggings, rapes, purse-snatchings, murders, break-ins, prostitution, juvenile delinquency and acts of outright vandalism all see huge increases. It's blackout crime-time and there are a dozen novels in this series.
The current publishers in English are: Orion Books, London; Soho Press, New York; and Allison and Busby, London.