Paris, March 1944. For days, black smoke has been pouring from the chimney of a locked townhouse on the rue Le Sueur, and the whole street can smell it.

When firemen force the shutters on the second floor, one of them comes back out and is sick in the doorway. A little later the doctor who owns the house rides up on a bicycle. Before he says anything else, he asks each policeman whether he is French. Then he pedals away into the dark.

The doctor was Marcel Petiot, and for more than two years in occupied Paris he had been selling a secret that couldn't be checked. For 25,000 francs he promised Jewish families in hiding, Resistance targets, and Paris gangsters a way out of France, through Spain and Portugal, and on to a new life in Argentina. His clients were told to turn their money into gold and jewels and sew their valuables into the linings of their clothes.

Joachim Guschinow was a furrier from the rue de Caumartin who left with five sable coats and diamonds sewn into his jacket. Kurt and Greta Kneller were German Jews in hiding with their young son René. Yvan Dreyfus was sent in by the Gestapo and vanished like the rest.

The rue Le Sueur today is a quiet street in the sixteenth arrondissement, off the Avenue Foch, not far from the Arc de Triomphe. Stand on the pavement at number 21 and you can see the join: the townhouse Petiot knew came down in 1954, and the building that replaced it is clearly of a different age. The basement below is said to survive. Nothing on the street marks what happened there.

Content warning: murder, antisemitism, the Nazi occupation of France, and the exploitation of refugees. Listener discretion advised.