Generally considered the first real giallo film, Mario Bava's stylish thriller stars Leticia Roman as Nora, who travels to Rome to visit her sick aunt. The aunt dies that night, and Nora ends up witnessing a murder. The police and kindly Dr. Bassi (John Saxon) don't believe her, since there is no body, so she goes to stay with her aunt's friends, the Cravens. Along the way, there are several more murders tied to a decade-long string of killings of victims chosen in alphabetical order by surname. The surprising ending is worth staying around for, as is an amusing supporting performance by Valentina Cortese. Bava would go on to further codify many of the giallo genre's conventions in Sei Donne per l'Assassino the following year.
by Robert Firsching synopsis