The film focuses on the infamous Boston Strangler murder case: from 1962 to 1964, 13 single women were attacked, sexually assaulted, and strangled in their apartments. After investigation, the police identified the suspect Albert DeSalvo, who pleaded guilty and was sentenced to life imprisonment, and was later killed in prison. There are many doubts in this case, and the real serial killer and the person who killed DeSalvo remain a mystery.