thelamplightersserenade asked: A noir storyline is characterized by normal people committing extraordinary crimes (Double Indemnity, The Letter). But there are mysteries all over "Best of noir" lists that are characterized by their whodunit storylines, like "The Maltese Falcon", "Laura", and "In a Lonely Place". Then there are the noir story lines that make no connection with the standard noirs; White Heat, Notorious. What is the difference?
This is one I should have answered long, long ago, so I apologize. But here’s the best answer I’ve been able to formulate in the interim:
Part of the problem is that film noir refers to both noir and hardboiled fiction (I cursorily sketch the differences between the two here). Noir is, of course, an offshoot of hardboiled crime fiction. But The Maltese Falcon (hardboiled classic) is called a film noir, just like Double Indemnity (noir classic). This explains some of the differences you note. (In a Lonely Place is noir, but the original novel by Dorothy B. Hughes has quite a bit of hardboiled dialogue.)
A further distinction is that film noir became a reference not only to the origin of the script, but also a visual style. Notorious is filmed in this style. I know relatively little about Vera Caspary, but what little I know indicates that she wrote neither hardboiled nor noir. Richard Condon wrote thrillers and satires, but not hardboiled/noir stories. But the film adaptions of Laura and The Manchurian Candidate used the film-making techniques associated with film noir (The Manchurian Candidate, made in 1962, is better termed a neo-noir—but that’s another can of worms entirely).
As a result, there is a great diversity of what could properly be noir. It depends whether one is talking of films or books, and chronology also plays a part (film noir proper is regarded as ending around 1958).