Leticia Roman is an American tourist in Rome who witnesses a murder. The dead body disappears so nobody believes her. She meets an Italian doctor, John Saxon, and together they try to find the killer.
This film is a mix of Hitchcock and Agatha Christie, but has also a touch of Roman Holiday. Leticia Roman is the first in a long line of stupid and hysterical girls in Italian giallo films, screaming their head off at the drop of a hat (She doesn't take her clothes off and take a shower, though). It reminds me of Gaslight, 1944, where Ingrid Bergman is so helpless, you can't help but end up rooting for Charles Boyer to drive her crazy. In the tradition of giallo it is the least likely person who is the killer, and in the same tradition the motive for the killing makes no sense at all. But the film looks great - it was Bava's last film to be shot in black and white.