Someone is firing a gun into a hotel suite to frighten guests. But who, and why? You'll never guess the "why" part. Set almost entirely indoors, "Midnight Warning" could easily be a stage play. Which isn't altogether bad. Though the script is indeed somewhat talky, there is a secondary mystery that gives the story thematic depth.
The script is not well written. An inspector that can read suspects' lips expedites the plot but his talent isn't believable as used here. The good guys always manage to be at the right place at the right time, a time-worn cliché. And as the plot proceeds, some of the male characters blend together, so they don't stand out well as unique or interesting. The morgue sequence near the end is just downright tacky.
Yet despite the script's overall poor quality, the story's underlying premise is effective, as the ending dialogue communicates a twist that puts the entire story into perspective. I had never before seen such a plot twist.
The worst element is the film's production. B&W cinematography is awful. The visuals are so dark there were scenes that I couldn't distinguish characters from a solid black background; all I could see were their white shirts. Annoying splotches appear in a few scenes, suggesting inferior film stock. And the crackling and static that overlaid the dialogue rendered poor sound quality. Of course one needs to take into account the inferior technology that existed in those early days of film-making. Production design, film direction, and acting are below average.
The underlying premise of "Midnight Warning" is thought provoking and interesting. But viewers will need to lower their expectations due to a substandard plot and dreadful production values.