Sound technician and inventor Dred Faraday enters a block-square, three-story municipal garage that has heavy metal roll-down grilles to block vehicle access in or out when it is closed for the night to test his special sound equipment that lets him echo-locate, listen from a distance, and play back and synthesize a wide range of sounds that he can make seem to come from any spot.
Faraday discovers that three kidnappers and their child hostage are there too, forced by circumstances to hide in there overnight but literally no one else knows that. Taking what he hears the kidnappers say seriously – that the hostage is safe as long as the trio believe no one knows where they are – Faraday tries to rescue the boy without bringing the police into it. He must keep them from escaping or harming the boy using the only the weapons he has available - a wide array of recorded and synthesized-on-the-spot sound effects - to confuse, frighten, reassure, or soothe the kidnappers as the moment requires.
Eventually he contacts a police ally who sneaks a SWAT team into the garage without the paranoid kidnappers realizing it. As the leader of the kidnappers goes to pieces from the strain though, it is up to Faraday and his sound tools to try to make the scene such a blast for her that she can’t kill the boy or anyone else.