Sam Dalmas , an American writer living in Rome, witnesses a brutal struggle between a young woman and also a black-coated figure in an art gallery, while walking home one day. Dalmas attempts to intervene but has been caught between your gallery operated glass doors, which makes the woman suffering from knife wounds. Questioned by the police, the shocked author attempts to recall every detail regarding the incident. Convinced that there is definitely an element of the crime they can't recall, Dalmas begins his own evaluation - putting himself and his girl friend Giulia in lineup as the killer potential sufferers...