The style is noir. Which is what inspired Jonathan Demme to take options on all four Easy Rawlins books, and turn this first one, Devil In A Blue Dress, into a movie. It will also help that Washington is not unattractive to women. The title devil is pretty bewitching, and she falls hard for Easy. Unlike the author's, perhaps.
Writing is an unconscious thing.
You write, and things come out, and then you rewrite and make it make sense. He thinks that's how he makes big decisions too. Like what storyline to follow. But I think for most writers, in or outside the genre, the plot comes when you know what you're writing about. I know everything about the book now, just from that line.