Cult Italian horror directed by Dario Argento. Young understudy Betty (Cristina Marsillach) is thrust into the limelight to play Lady Macbeth after an accident forces the main star out of the production. Despite her initial reservations her opening performance is lauded. However, there follows a series of brutal murders that Betty is made to bear witness to and as the killings continue she suspects that the killer may be someone she knows.