The Maltese Falcon, based on Dashiell Hammett's novel of the same name, is Exhibit A for the film noir genre. It was also, decades ago, the first Humphrey Bogart movie I ever saw. Bogart plays Sam Spade, a San Francisco PI who gets mixed up with sinister characters, all in search of "the bird," a golden, bejeweled falcon statuette worth an unfathomable fortune.
The acting is good and the writing excellent. Apart from all of the devices which would come to define the form - shadows, silhouettes, morally ambiguous characters - much of the fun of the story is watching the abrupt shifts in power dynamics within a single scene. I enjoy the film and respect its stature within the medium but it's not one I feel compelled to watch repeatedly.