There are two killers. The first is revaled to be one of the victims, Christiano Berti (John Steiner), an obsessed fan of writer Peter Neal (Anthony Franciosa) and who was behind the phone calls and letters. Neal murdered Berti and then out of his own insanity, took over Berti's killing spree by killing Bulmer (John Saxon) and Neal's ex-wife Jane (Veronica Lario) whom was having an affair with Bulmer. Neal gets the upper hand against both detectives and axes them too. But Neal is killed in an accident when he gets impaled by a steel spike that falls off a sculpture before he can kill his secretary Anne (Daria Nicolodi).
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