When the leading diva of Verdi's "Macbeth" is run over by a car, her understudy, Betty (Cristina Marsillach), takes over the role. Things go from bad to worse when a madman begins to kill other members of the cast -- and forces Betty to watch. As the police struggle to find the murderer, Betty begins to realize her death will be the final act if they can't locate the killer in time. Dario Argento directs.