The beginning is rather like "Murder, My Sweet"--Phillip Marlowe, or in this case Johnny Smith, is debriefed by the cops, and thus narrates the events of the story. From there, we see many conventions of film noir--the crime boss the hero is forced, through fate, to get involved with...the femme fatale, who drives the hero to change everything...all the way down to Johnny going all Mike Hammer on Sonny!
The conflict with Walt is very interesting. I never understood why Johnny never reveals all of his suspicions--let alone his discoveries--about Stilson to Walt and Sarah. Especially considering Sarah working for the man. Why doesn't he just tell Walt everything he knows?
Sarah's exchange with Johnny is also very telling. She knows Stilson's rotten--but is under the impression that, as his conscience, she can set him straight--that she is Dick Morris to Sonny's James Carville...with Clinton/Stilson in the middle.