Carroll Baker, the blond starlet best known for her role in Baby Doll, ended her career in a number of Italian giallo thrillers including A Quiet Place to Kill, Paranoia, The Fourth Victim, and this giallo-tinged crime film from director Osvaldo Civirani. Baker plays a dual role as translator Julie Harrison and her twin sister Mary. The serpentine plot begins as Julie tells her lawyer Dave Barton (Stephen Boyd from Ben-Hur) that Mary's life is being threatened in London while Julie herself is being stalked by a mysterious stranger in Amsterdam. Dave's racecar-driving friend Tony Shane (George Hilton) saves her from both an attempted kidnapping and an attempted murder before putting her up with an old blind woman to hide. The blind woman is murdered that same night, and Luciano Pigozzi turns up as an insurance investigator who finds out that Mary has stolen a precious diamond from an Indian Maharaja, double-crossing her husband to do so.