Seventeen-year-old Mary Ann Markham and her best friend, Jennifer Martin, decide to audition with a local amateur theatrical group. They plan to drag along Art Parker, Mary Ann's adoptive father, until they discover that the tryouts have been postponed because of a dead body cluttering the stage. Never ones to be thwarted in their pursuits by a few extraneous corpses, they soon find themselves involved in trying to identify a clever murderer who seems hell-bent on wiping out actors and stage crew alike. They survive a severe thunderstorm in an abandoned gristmill only to find themselves a target for the killer as well as for a big black dog named Satan.