Idea for a movie

Here's a quick idea for a movie script I'm thinking of and don't want to forget. It's called "The Story Not Told." The concept is that there is a pretty good and clear noire detective story -- in fact I might even set it in the 40s or 50s. It's a first person narrative with voice-over. We follow the detective as he pieces together his puzzle, but in almost every shot there is a different cast acting out a completely different story in the background. Some of the characters overlap, so they come into focus as part of the story the detective is telling, but the untold story is unfolding in the background and in the wasted scenes of most movies. It is the people passing in the park, kissing in a doorway, seen at the hospital, or in the bar, and at the police station. So the key will be to have the other story unfold completely and with a full resolution without any scenes or dialog actually attributed to it. Yeah!