Infamous burglar "The Bat" commits a daring jewelry theft despite heavy police presence. Soon after, a bank theft occurs, which may be the work of the criminal as well. Meanwhile, Cornelia Van Gorder (Grayce Hampton) has various people arrive at her old mansion, including her niece, Dale (Una Merkel), a bank employee, and police detective Anderson (Chester Morris). When guests start turning up dead, Cornelia begins to suspect that The Bat may be lurking around the estate.