The classic A-feature (e.g. Murder, My Sweet) revolves around a hero whose attention is divided between a plain, brunette "good girl" (Anne Riodan) and a glamorous blonde femme fatale. Detour, in contrast features a good girl who is a blonde and glamorous singer and who the hero loves. The femme fatale is a "good girl gone wrong" whom he describes as possessing, "a beauty almost homely, its so real." This reverses the typical situation: Vera's character, founded on the "good girl" stereotype but exhibiting the behaviour of the femme fatale, implies that all women pose a threat to men and male dominance.
The revelation of the femme fatale's moral turpitude is also inverted. Taking Murder, My Sweet's Mrs. Grayle as archetypal, the femme fatale's usual method of subjecting the hero to her will is to seduce and flatter him until a relationship is formed on the basis of sexual addition and misplaced trust. It is only later the she is glimpsed in her true light as manipulative and sadistic. Vera is quite different. She is immediately and openly hostile to Al and never relents, never believes his innocence. This disparity with A-features makes Vera seem like a harsh dose of reality in contrast to a romanticised stock-character. At least Phyllis Dietrichson's actions were intended to improve her future, and may be aligned with optimistic concepts of the American dream and individual enterprise. Vera has no future - she is dying of a fatal illness - and her imprisoning of Al is motivated by a more vindictive spirit, a sadistic impulse. She has nothing to gain but doesn't want to suffer alone.
All films noirs can be seen to dramatise male post-war anxiety about women assuming a more dominant position in society. The femme fatale embodies this concept, while heroes mirror the dismay felt by veterans returning home to find women in an alarming position of authority. Detour depicts this anxiety in extremis. Unlike the A-feature hero (Spade and Marlowe) Al's identity is not merely threatened by the femme fatale and finally wrested from her clutches (as in The Maltese Falcon). Al literally loses his identity, shedding it to take temporary refuge in Haskell's. This is symbolised by exchanging his clothes for Haskell's, but results in Al's arrest because he has also acquired his past sins, giving a dark, haunted tone to his impersonation.
Al is conspicuously less heroic than his A-feature counterparts Spade and Marlowe, both of whom are struggling for the eventual triumph of justice. Their actions are motivated by a hope for a better society; Al has no such enthusiasm. This is evident in his dismissal of Sue's hopes he will someday play at Carnegie Hall and his incessant self-pitying narration. Detour has no hero, the mood is one of constant despair, evoking a world in which there is nothing the individual can do since it "will outlast and negate even his best efforts."
In conclusion, though elements of darkness pervade all films noirs, whether A or B- features, Detour exhibits an unprecedented facility for exploiting its low budget to darkening effect. The result is a darker film which is more in tune with the noir spirit, and which is free to present subversive values in accordance with a contemporary trend felt by many in the wake of World War Two, and identified by Paul Schrader: "audiences and artists were now eager to take a less optimistic view of things". Central to this is Vera, who inverts a traditional film noir concept to create a viciously darker femme fatale. Detour's narrative structure adapts that of the typical film noir to allow a near-psychotic narrator to imbue each event with a hallucinatory and sordid noirceur.
