Unlike the other classic masters of crime fiction (Hammett, Chandler, and even Christie if you must) James M Cain wrote not from the perspective of the cop, or the detective, but from the side of the criminal. He wasn't really interested in the methods of detection, but in the methods and reasons crimes were committed.
There are no Christopher Marlowes or Hercule Poirots out to solve the case in Cain's fiction. The righteous bringers of justice are regulated to a secondhand role in his stories, and are often as slimy and unrighteous as the criminals.
In his first novel, The Postman Always Rings Twice, Cain weaves a complicated plot in a very simple manner. This was never meant as anything more than a pulp novel, it's aim was to titillate, shock, and most important of all, sell gobs of books.
Though told in the first person from a main character, the book is all action. There is some internal dialog, but it sheds very little light on who the characters are, what motivates them.
It is in fact, perfect for a screen adaptation. Which is probably why it is credited as the story on at least 5 times on the Internet Movie Database. The lack of complicated internal though processes, and the predilection for talking and doing, makes it the ideal movie. That, and great lumps of sex and violence.
The two most famous screen adaptations are the 1946 Lana Turner/John Garfield version and the steamier Jack Nicholson/Jessica Lange released in 1981. Everyone refers to that one as a remake of the 1946 version which gets me riled up for some reason. To me it is simply another version of the novel, rather than a remake of the old film. There are about 8 million versions of Hamlet out there, but no one refers to the next one as a remake of an earlier film. It's simply another version of the play. But perhaps this is because I'm a fan of the novel, and I probably shouldn't make too big a deal out of it.
The plot takes on several turns but is essentially about lust and violence. Drifter Frank Chambers lands a job at a road side diner owned by Nick Papadakis (Smith in the 1946 version). Chambers falls immediately in lust with Nick's unhappy wife, Cora. They cook up a plot to kill Nick making it look like an accident. Complications ensue.