When several middle-aged women are found strangled and sexually assaulted in the Back Bay area of Boston, the police round up numerous suspects but fail to uncover any leads. As the stranglings continue, Massachusetts Atty. Gen. Edward W. Brooke, Jr., persuades Asst. Atty. Gen. John S. Bottomly to set up a bureau to coordinate information concerning the slayings. While women report possible suspects, an ESP expert, Peter Hurkos, is brought in to conjure up a vision of the murderer. Elsewhere in the city, plumber Albert DeSalvo stops watching the funeral of President Kennedy on television and tells his wife that he must check on a customer's furnace. Instead, he gains access to a young woman's home and murders her. He continues his attacks but is finally apprehended when he is chased into the street by the husband of an intended victim and struck by a police car. DeSalvo is sent to Boston City Hospital for observation, while Bottomly and Det. Phillip J. DiNatale question a surviving victim who recalls that she bit her attacker on the thumb. Discovering that DeSalvo has a bite mark on his thumb, Bottomly and DiNatale check his place of employment and discover that his absences from work correspond with the dates of the murders. Aware that DeSalvo may be a schizophrenic incapable of total recall, Bottomly places him in a room with his wife and watches from behind a glass wall as the confrontation triggers DeSalvo's subconscious and compels him to clutch his wife by the throat. There is insufficient evidence to prove that DeSalvo is the strangler, but Bottomly is certain that he has the right man when DeSalvo later reveals additional details about the murders.