Ketty, a photographer living in Rome, accidentally witnesses the murder of a young woman at the hands of a razor-wielding maniac. Ketty and her fiance, Alberto, go to the police--only to learn that two other witnesses to the crime have been slashed to death. Ketty fears that she will be the next victim when her ballerina friend Magda is brutally killed by the same elusive culprit. The police are baffled, unable to find a motive. It is Alberto who discovers the connection: all the murdered girls were dancers. Investigating further, Ketty finds a photo identifying the killer. But before she can warn Alberto, Ketty is trapped in a lonely greenhouse, stalked by the homicidal madman!