I'm writing this before I've finished the book, so I don't know the outcome and how it will play out, but here goes nevertheless.
Jack Williamson's Darker Than You Think (published first in 1940 in Unknown, then in book form in 1948) is a werewolf classic and as such it seems dated now, though it must've been pretty ground-breaking at the time, for all its realism and psychological acuteness. Williamson even strives for a plausible explanation of lycanthropy, but the explanation of course seems dated now.
The title of the book is a lot like many film noirs with its emphasis on dark, and sure enough one could see this as a film noir, especially with the red-haired femme fatale of the book, April Bell. The hero of the book, Will Barbee, is an ordinary sap, hacking newspaper stories and drinking whiskey and waking up to a nightmare of his life.
More Forgotten Books here at Patti Abbott's blog. There's an Elmore Leonard week, but I wasn't able to participate in that.