The Maltese Falcon was published in 1929, twelve years before Humphrey Bogart played Sam Spade. In the book, Spade and Brigid O’Shaughnessy have sex, Spade has blond hair and Casper Gutman (the fat man) has a daughter. Other than that, the book and movie are quite similar. The movie even borrows a lot of dialogue from the book, which is a good thing, because Hammett’s dialogue is excellent.
Spade spends most of the novel wandering around San Francisco trying to figure things out. Brigid O’Shaughnessy shares as little information as possible, but since they do spend one night together, it makes more sense in the book than the movie when Spade talks about them being in love. Although she still has to take the fall, of course.