To some, crime noir is a subgenre set in grim urban environments, featuring petty criminals and desperate characters, permeated by a sense of disillusionment. I favour a wider lens. In the North Noir (Detective Naslund) series, crime noir is less bleak. It is more like life itself: not always dark, not always light.
Crime noir is linked to film noir, to movies such as The Maltese Falcon, which was first a novel. In a noir detective novel, the main character is sharp-witted and/or sharp-tongued. No quarter is given. Criminals try to rig the system, but fail.
Of course, noir detectives aren’t lily white. They cross lines, some more egregious than others, which they breach for the sake of efficiency or to apprehend criminals. Noir detectives are crime fiction’s dark angels. They know darkness, but follow the light.