A private detective's business exists in a tricky paradox. He has to earn the loyalty of his clients, but his clients also have to earn his trust. He has to form alliances and partnerships with sources, but these same sources (who are usually criminals of some sort) could sell him out at a moment's notice. Even his own clients might be trying to take advantage of him.
In the dark world of film noir, anyone's loyalty is up for sale. No wonder most of The Maltese Falcon takes place at night. We wouldn't be able to sleep either, if we always had to watch our backs.
Brigid feels betrayed by Spade (there's a good fan fic title for you) in the end, but she never had his loyalty to begin with. He only tricked her into thinking that she did.
The only people in the movie who are truly loyal to one another are Spade and Effie. He always puts his career first, and she is critical to his job.
A detective's job is sniffing out lies. Anyone could be lying to him at any time—his partner, the person he's investigating, or even his client. Sam Spade of The Maltese Falcon has a pretty good sniffer, but it isn't without a blind spot or two.
Wait—what's a blind spot when it comes to your nose? It's called a "congestion zone." Would we lie to you?
Spade is just as deceitful as Brigid it, playing all sides—her, Gutman, and the cops. But he has a self-justification for why he does it.
The Maltese Falcon is deceitful. Even the real one is a lie because it's a gold statue bedazzled with gemstones and coated with black enamel to disguise its true nature.
The Maltese Falcon is the Tickle Me Elmo of the 1940s. Certain people will trample you, sell you out, or set a cargo ship on fire to get their grubby mitts on it.
The difference between the Falcon and Tickle Me Elmo is that there's only one Maltese Falcon, so it has significant value…or at least so we thought. Gutman ends up with a counterfeit Falcon, meaning his quest might never come to an end. Like a knock-off Tickle My Elbow doll, the counterfeit is completely worthless.
Some people, like Brigid and Cairo, are after the Falcon because of its monetary value. Gutman, however, appears to be in it for the thrill of the chase.
Spade is a man who is greedy not for wealth, but for love, or maybe lust. He takes his partner's wife, and he would rather have Brigid instead of the Falcon…at least until the end of the movie.
It's appropriate that The Maltese Falcon is in black and white, because Detective Sam Spade lives in the wide gray area between legality and criminality. He isn't a virtuous detective like the pie maker from Pushing Daises or Mma Ramotswe from The No. 1 Ladies' Detective Agency. Spade is a detective who isn't afraid to get his hands dirty…like a shovel. Spade. Shovel. Get it?
Spade tends to side with the criminal element more often than he sides with the cops, but he never gets himself in too deep that he could be considered a criminal himself. There's a blurry line between associating with criminals and being a criminal, and Spade must always make sure the cops know he is firmly on the legal side of that line.
For Spade, who rides the line, he does believe there is a line that cannot be crossed, and that line is murder (or, specifically, murdering his partner). Once he finds out that Brigid kills Archer, he turns her in. The man has his limits.