In an important essay James Demico wrote that the typical noir narrative involves:

A man whose experience of life has left him sanguine and bitter [and who] meets a not-innocent woman of similar outlook to whom he is sexually and fatally attracted. Through this attraction, either because the woman induces him to it or because it is the natural result of their relationship, the man comes to cheat, attempt to murder or actually murder a second man to whom the woman is unhappily or unwillingly attached (generally he is her husband or lover), an act which brings about the sometimes metaphoric but usually literal destruction of the woman, the man to whom she is attached and frequently the protagonist himself.

The narrative of a typical A-noir, Double Indemnity, follows this outline very closely: Walter Neff is seduced by Phyllis Dietrichson and persuaded to kill her husband. After the murder their relationship deteriorates, culminating in a mutual shooting. Detour passes all these signposts - the disillusioned protagonist (Al), the femme fatale (Vera), the dead man to whom she is attached (Haskell). But there are several important differences which make Detour's narrative even more tragic and deplorable. Firstly, the man in Vera's past is not her husband but a driver who stopped for her while she was hitchhiking, and whose aggressive attempts at seduction forced her to retaliate by scarring his hand. He is therefore far from being the wronged husband of Double Indemnity.

Haskell's death is accidental. This might suggest that it is free of the dark overtones of Double Indemnity. Noirceur, however, resumes its dominance by the fact that the event still initiates Al's destruction, despite his innocence. While Neff was persuaded to commit murder, and therefore deserved his end, Al is simply an honest man who became involved by chance and hasn't yet met Vera. The blame for his downfall cannot therefore reside with an immoral woman who is punished at the conclusion of the narrative with death, thereby ensuring that justice is done. In Detour there is no justice, only luck ('Sure, all bad!'). It is the notion that Al is a victim of cruel fate rather than a cruel protagonist that gives Detour its dark resonance. Clearly, the "mysterious force" Al feverishly warns us of is more formidable than the machinations of any single character.

In many ways this narrative had been dictated by economic factors, and much of Detour's noirceur can be seen to derive from budgetary considerations. Paul Kerr has noted that "B units [were] compelled to carve our distinctive and identifiable styles for themselves in order to differentiate their product." This led to Detour becoming overtly noir in order to stand out among top-billing A-features. It achieved this to such an extent that Hossein Amini has written, "even the label film noir doesn"t do justice to the sheer blackness that pervades its story.'

Detour employs only three sets, plus some location shooting and stock footage. It is feasible that Martin Goldsmith may have based his script around scenarios that induce an intense claustrophobia, since these would require minimal sets, props, costumes, and actors, and would not strain the budget. The result is several lengthy interior scenes such as that in the hotel room, in which only two characters feature. This scene's purpose is to depict Al's claustrophobic reaction to being imprisoned by Vera, an effect which Detour, with its paucity of production values, was ideally suited for. The cramped, impoverished set highlights Al and Vera's drastic situation as they eke out the money stolen from Haskell. Each character wears only one costume for the majority of the film, and Al in particular becomes increasingly dishevelled. This emphasises their sense of being destitute and on the run. Kim Newman has written, "this is a film whose literal poverty seeps into every frame, suggesting the nightmare of a main character whose very life is low budget."

As well as being cheaper, low-key lighting in many scenes invests them with the fatalistic, restless mood characteristic of both A and B noirs. But Detour takes the technique to extremes. When Al is informed by his girlfriend, Sue, that she is leaving him for Hollywood, the scene is conducted in an oppressive black welter of darkness and fog. The sifting clouds of blackness seem to forebode of Al's imminent destruction, obscuring him as Sue walks away and leaving him groping about for answers. The severance of their relationship, and Al's dark fate, is emphasised when the light above the nightclub door is extinguished as they leave.

This scene appears to have been filmed at night, with only enough lighting to pick out the actors. B-movies frequently had short shooting schedules since equipment was often rented. For Detour, famously shot in six days, night-shooting would have been obligatory. Genuine "night-for-night" shooting gave a deeper blackness than the twilight-shooting used in A-features (e.g. Marriott's murder in Murder, My Sweet). Detour's paucity can thus be understood as creating an effect that is much more congruent with the noir spirit than are the conventions of A-feature production.

While it is more archetypally noir, this scene is scarcely realistic, the fog seeming rather theatrical. But instead of detracting from the scene's effectiveness, the highly stylised setting enhances it. It is conducive to a more "artistic" mode of filmmaking than conventional Hollywood is generally perceived to be. The overt theatricality of these scenes has been interpreted in the distorted light of German Expressionism. Detour's director, Edgar G. Ulmer, was an assistant to Expressionist auteurs Murnau and Lang, and his films (along with noir in general) show their influence in the use of chiaroscuro and oblique lines. Some commentators have even suggested that low budgets encouraged B-units to "compensate with complicated plots and convoluted atmosphere. Realist denotation would have thus been de-emphasised in favour of expressionist connotation." This argument lends credibility to the suggestion Goldsmith's script deliberately focussed on situations that a low budget would not hinder. The use of Al's confessional monologue triggers highly subjective flashbacks with a paranoid, hallucinatory feel. Certain cheaply executed effects, such as the giant cardboard coffee cup and the constrictive night of a back-projection machine, evoke his increasing delirium, giving a dark and harassed quality to the film. At one point Al announces that we probably don't believe his story. This generates a sense that he is not a dependable and objective surrogate for the audience in the way that Philip Marlowe is. The A-feature hero remains untarnished by his experiences, while Al's are more corrupting and hopeless. His monologue is not a rational account of events delivered to the police (as in Murder, My Sweet) but a confession blurred by self-pity and elaboration. The lack of a lucid, shared viewpoint between audience and protagonist contributes to Detour'snoirceur by negating any faith in the hero or his explanation. Al's remark generates the suspicion that every flashback (i.e. most of the film) could be a lie. profound

These features perhaps verify the view that "as a “poverty row quickie,” Detour is a film that does not need to affirm conventional values and can embrace the subversive implications of film noir more completely than many more obviously distinguished productions." Central to this is a rebuke of the "American dream" that is unrivalled by the noirceur of typical A-features. Double Indemnity (and Scarface and Public Enemy) exhibits a private enterprise ethos that solicits audience sympathy for the criminals. These A-features seem to be dramatised accounts of the chase for the illusive notion of the American dream. They are escapist entertainment, and their depiction of a character prepared to do anything in order to succeed causes them to exude the same romantically tragic fascination of Gatsby's green light. Of course, they also imposed a conventional "crime-doesn"t-pay' death-scene as a moral condemnation of the criminal's activities. Detour has no such moral closure: Al's arrest, rather than death, is shrouded in ambiguity and redolent with the fear of an uncertain fate. Furthermore, Al has no similar urge to succeed. From the very beginning he demonstrates a fatalistic and cynical outlook as well as signs of mental instability: observe his crazed interpretation of a Brahm's waltz at the piano. Therefore, even before he has become embroiled in the noir scenario he has rejected the American dream and been beaten into submission by the overwhelming harshness of the world. This is manifested in his scorn for things normally indicative to the American dream: his incomprehension of Sue's desire for fame; his abhorrence of money ('What was it? A piece of paper crawling with germs.') and his use of baseball metaphors to lament the state of the world, baseball usually being associated with aspiration.

An important aspect of Detour, and one without which no film noir would be complete, is the presence of the femme fatale. Vera fulfils this role, but her character differs significantly from the traditional fatal woman of A-features such as Murder, My Sweet and The Maltese Falcon. One reason for this is a resurgence of the economic determinism already discussed. Vera is just as destitute as Al, a detail that may have been written into the script so that her costume would not look out of place. She has been described as a "skid row femme fatale," and, as well as being cheaper, this is somehow more realistic and less romantic than the glamorous sirens of fashion-conscious A-features. Accordingly, Vera inverts the traditional femme fatale role.

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.