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One of the final links between the Edgar Wallace-based German krimi genre and the Italian giallo thriller, this creepy mystery stars Fabio Testi as a college professor who sleeps with his students and is blamed when a string of murders occurs. Joachim Fuchsberger, as usual, is the police inspector trying to solve the killings; Camille Keaton, Buster Keaton's grand-niece and later the star of Meir Zarchi's I Spit on Your Grave (1980) has a supporting role; cameraman Aristide Massaccesi, later infamous as gore director "Joe D'Amato," turns up as a cop. Massimo Dallamano's direction is assured. This first-rate thriller was based on Wallace's Secret of the Green Pin.