Roaming through the old mediaeval town he encounters Sylvie, a mysterious young woman who was adopted as an orphaned child by M. Toulzac, a former teacher now confined to a wheelchair.

The film was based on a short story, La mort ne reçoit que sur rendez-vous ("Death only receives by appointment"), by Gaston Bonheur, published in Paris-soir (Toulouse) in 1943.

Bonheur and the director Serge de Poligny made the screen adaptation with contributions by Henri Calef (in hiding because of his Jewish origins) and Jean Anouilh (who wrote the love-scene on the ramparts of Carcassonne).

The confrontation between the mediaeval world and modern reality is a recurrent theme in both the story and the visual style (the opening shot juxtaposes the old and new towns of Carcassonne).

The unusual and original nature of the themes of La Fiancée des ténèbres, at a time when there was little knowledge of Catharism, and its disconcerting contrasts of tone meant that it was greeted with widespread incomprehension by both audiences and critics.

It included this assessment of La Fiancée des ténèbres:[5][3] In the history of French cinema there is a film which is universally regarded today as the first and only one to have been inspired by the Cathars.

Greeted with sneers at the time of its release amid general incomprehension, on account of the labyrinthine complexity of a screenplay loaded with cultural references; admired for the formal perfection of its imagery, today La Fiancée des ténèbres surprises and fascinates the young generations of spectators who are more aware of questions of the irrational and also more receptive to a narrative which breaks with the over-literary conventions of 1930s cinema.