This is Truffaut's last film before his untimely death at age 52. It is a conscious homage to Hitchcock, shot on purpose in black and white, and at the same time a vehicle for Fanny Ardent, the actress with whom he shared his life at that time. The story was taken from an American pulp thriller (The Long Saturday Night by Charles Williams) - Truffaut used more pulp stories in his films, for example in Shoot the Pianist and in The Bride Wore Black.
The story is fluffy and improbable, but the glamorous Fanny Ardent carries the film. She is a woman in a world of men, and dark-haired in a world where blondes are popular. There are several conscious references to Hitchcock, such as legs passing in the street seen from below through a cellar window. A diffidence with Hitchcock is that where the elder master disliked women and usually cast icy and mean blondes, Truffaut admired women.
[Fanny Ardent - Photo Wikipedia]
The film is humorous rather than dark - I would not call this a film-noir, although it plays with some noir elements. It lacks the femme fatale, the hero does not fall into a trap which only gets worse, and the ending is optimistic. It is a fun film perfect in its genre.