Eight people, all of whom have reason to hate at least some of the others, are invited by a mysterious unknown host to spend the night in a penthouse apartment. After the five men and three women are wined and dined, they're greeted by their host's voice via a radio broadcast. The voice announces that before the night is over, each one will be systematically murdered unless they manage to outwit their ninth guest: Death. Based on the mystery novel "The Invisible Host" (1930) by Gwen Bristow and Bruce Manning.