An old man is walking his dog in New York City when the dog retrieves a decomposed human hand. It is identified by the police as belonging to Ann-Lynne, a local prostitute. Lieutenant Fred Williams (Jack Hedley), the burned-out police detective investigating the murder, interviews the young woman's nosy and obnoxious landlady, Mrs. Weissburger (Babette New), who tells him that during her daily spying and eavesdropping on her tenants, she overheard the girl last week over the phone arranging to meet a man who spoke with a strange, duck-like voice.
Meanwhile, a young woman (Cinzia de Ponti) rides her bicycle down Manhattan to the Staten Island Ferry at Battery Park. After an altercation with a boorish motorist driving a red Volkswagen, whose car she accidentally scratched riding her bicycle, she rides onto the boat with the man yelling misogynist slurs at her. When the ferry is underway, the young woman sneaks into the car-bay and begins vandalizing the man's car, but she is interrupted by an unseen figure. Introducing herself as Rosie, she tries to engage the man in a conversation. But the figure adopts a grotesque 'Donald Duck' voice and brutally murders her with a switchblade, slashing open her right breast, stabbing her in the lower abdomen and disemboweling her, and cutting her throat, then leaving her body to be discovered when the ferry docks at Staten Island. At the morgue, Lt. Williams talks to Barry Jones the pathologist (Giordano Falzoni), who believes he recognizes the "style" of the killing and links it to Ann-Lynne, as well as a similar case in Harlem the previous month.
Having informed the press that a serial killer is at large, Williams is visited at the station by New York's chief of police (Lucio Fulci). Williams' skeptical superior tells him not to make any further public announcements about the case to avoid starting a citywide panic. Soon after the police chief leaves, Williams is notified that a man "sounding like a duck" phoned while he was out at the press conference wanting to speak with him. Williams travels to Columbia University where he meets with a brilliant young psychotherapy professor named Dr. Paul Davis (Paolo Malco) for help in creating a profile of the killer.
That night in New York's red-light district, Jane Lodge (Alexandra Delli Colli), an attractive, well-dressed woman in a chic raincoat and derby hat, attends a live sex show and records the simulated moans and groans of the two performers with a pocket tape recorder. A scruffy, dangerous looking man (Howard Ross), with two fingers missing from his right hand and sitting in the same row with her, observes what she is doing. After the show has ended, the female performer (Zora Kerova) retires backstage to her dressing room only to find it totally dark. Hearing a noise, she opens a closet door and is brutally attacked by the maniac, who disembowels her by shoving a broken and jagged liquor bottle from her crotch to her abdomen. Later that night, at the home of Kitty (Daniela Doria), a prostitute regularly visited by Williams, he receives a taunting phone call from the duck-voiced killer saying that he has killed again.
The next day, Jane shows her latest tape recording to her husband Dr. Lodge (Laurence Welles), who has agreed to support their open-marriage. Jane goes to a bar in a rough neighborhood where she's approached by two Hispanic bar punks who proceed to fondle and sexually humiliate her right at the bar. After being taken advantage of, the emotionally troubled Jane runs out and drives away.
That night, Fay Majors (Almanta Keller), a casually dressed young woman is riding alone on a late-night subway train when she gets menaced by the same ominous man from the live sex theater. Fleeing from the perceived threat, she runs off the train, through the deserted subway station, and onto the street where she gets attacked in a dark alley by the quacking maniac, who brutally stabs her in the leg and slashes her hands and arms as she tries to defend herself. Limping away, Fay stumbles through a doorway into a seedy apartment building where she closes and locks the door behind her so the killer will not follow. Fay passes out from the loss of blood, and then realty and illusion blur: Fay is sitting alone in a dark movie theater watching cartoons when she attacked and killed by a different, handsome young man who slashes her neck with a straight razor. Fay wakes up in the hospital the morning after when the same man visits her in her room. The man is revealed to be her physicist boyfriend Peter Bunch (Andrew Painter), who is relieved that she has survived the attack. Lt. Williams and Dr. Davis visit Fay where she tells them about her attacker who was missing two fingers from his right hand. Williams and Davis both conclude that this is the killer since all forensic evidence points to the killer being left-handed.
Somewhere in night-time New York, the owner of his mutilated right hand picks up Jane and takes her to a sleazy hotel room for bondage sex. He ties up the semi-nude woman to the bed. The S&M game she has willingly begun turns nasty when he begins to beat her. Then the man turns up the radio loud while it plays Berto Pisano's "Tic nervoso" and makes a muttered phone-call, describing the bound woman to someone on the other line as "she's right up your perverted alley. " A little later, while the man sleeps, Jane overhears a radio DJ describing the killer, whom the press has now dubbed, 'the New York Ripper,' and missing two fingers from his right hand. Jane carefully and quietly unties herself from the bed and flees into the hotel hallway, only to be killed by the real New York Ripper, who guts her, and stabs her to death just as she tries to make for the exit at the end of the hall.
Williams arrives at the scene of the crime where the police find Jane's tape recordings of the sex shows and of her 'master.' Learning from witnesses, Williams discovers that the identity of the man is Mickey Scellenda, a Greek immigrant with a history of sexual assault and drug abuse. Williams and the police step up the search for Scellenda after raiding his apartment, finding photographs of most of the Ripper victims and huge stashes of pornography and drug paraphernalia. Williams also pays a visit to Dr. Lodge to inform him of his wife's murder. Dr. Lodge tearfully defends his open marriage which gets him a sneering response from the moralistic Williams.
Meanwhile, Dr. Davis begins to express doubt to the killer's identity, for Mickey Scellenda is only a petty criminal with a low intelligence quotient, not the high intelligence that Davis has established in profiling the New York Ripper. Davis then buys a gay porn magazine at a local newsstand (revealing his repressed homosexuality), and pays a visit to Peter and Fay at their house to ask them more questions about Fay's experience. Something about their story arouses his professional suspicious. That evening, after Peter goes out, Fay is attacked in their house by Scellenda who breaks in trying to kill her. But she is saved when Peter returns, and the man flees.
A few days later, Williams gets another taunting phone call from the New York Ripper, who wants to "dedicate a murder" to him. Williams and the police put a trace on the line and race to the location, only to find that the killer has set up a two-way radio to a remote phone booth, while he is presently in the home of Kitty, the young prostitute favored by Williams, brutally torturing her by slowly applying a razorblade to her bare chest and her face. Williams races to Kitty's apartment, but is too late as the killer has fled, leaving behind Kitty's horribly maimed corpse to be discovered.
Some time later, the dead body of Mickey Scellenda is found having committed suicide from self-suffocation. When Dr. Barry Jones informs Williams that Scellenda was dead for the last eight days, four days before Kitty's murder, Williams finally realizes that they have been tailing the wrong man. Williams relays this to Professor Davis, who is both delighted and disappointed with the news. Davis explains that with Scellenda eliminated as a suspect, his original idea to the killer's identity is confirmed; a misogynist psychopath who used Scellenda to throw the police off his trail.
Fay is shown visiting a hospital where Peter has a child from a previous marriage, a little girl named Suzy, who is dying from a rare bone disorder that has led to the amputation of her left arm and right leg. Visiting the hospital, Williams and Davis observe little Suzy in her hospital bed and decide to race over to Peter and Fay's place to arrest both of them. At Peter and Fay's house, one of them gets a phone call from a duck-voiced person, while the other one overhears. When Peter goes into the kitchen for dinner, Fay has disappeared. Going upstairs to Suzy's bedroom, Fay jumps out of the darkness at Peter while stabbing him with a kitchen knife. Suddenly, Peter rises, quacking like a duck, and struggles with Fay in which they both tumble down the stairs. Just as Peter grabs the knife away from Fay and about to stab her, Williams runs in and literally blasts Peter's face off with one shot from his gun. In the ambulance, Davis explains to Fay her deranged boyfriend's motivation for killing. His hatred of sexually active women stemmed from bitterness at the cruel blow fate had dealt his young daughter, who will never enjoy the freedoms of his despised victims. After leaving the scene, the phone in the now-deserted house rings again. In her hospital bed, little Suzy is calling out for her father, pleading to him to answer her call, as her voice is drowned out beneath the indifferent traffic of the city.Jack Hedley as Lt. Fred Williams
Paolo Malco as Dr. Paul Davis
Almanta Suska as Fay Majors (credited as Almanta Keller)
Howard Ross as Mickey Scellenda (Mikis)
Andrea Occhipinti as Peter Bunch (credited as Andrew Painter)
Alexandra Delli Colli as Jane Lodge
Cosimo Cinieri as Dr. Lodge (credited as Laurence Welles)
Giordano Falzoni as Dr. Barry Jones, Coroner
Daniela Doria as Kitty
Cinzia de Ponti as Rosie - Ferry victim
Zora Kerova as Eva - Sex show performer (credited as Zora Kerowa)
Josh Cruze as Chico (credited as Johs Cruze)
Antone Pagan as Morales (credited as Anthon Kagan)
Chiara Ferrari as Susy Bunch
Barbara Cupisti as Heather
The New York Ripper was poorly received by critics. AllMovie's review of the film was very negative, writing, "Pandering to the lowest common denominator as never before in his career, Fulci showed with this blatant play for the sicko slasher crowd that the days of well-plotted, stylish Italian horror were gone, replaced with the most vicious sort of sexual violence and perversion." Slant Magazine called it "sour and pointless".
Failing to secure a theatrical release in the United States, the film's home video debut there occurred belatedly in 1987 with a VHS tape issued from Vidmark Home Entertainment in an edited 88-minute cut that left most of the violence intact but removed much of the on-screen sexual activity.
In the UK the film was refused a theatrical certificate in 1982 by BBFC chairman James Ferman, who then re-exported the print to its original rights holder in Italy. Following Ferman's departure as chief censor it was released on VHS by Vipco in 2002 with cuts to the infamous breast-slashing scene, and all subsequent UK DVD releases have received the same cuts.
The film's first uncut widescreen presentation on home video surfaced in 1994 in an English language laserdisc release manufactured in the Netherlands by Professional Cine Media.
The film has been released on DVD in America by Anchor Bay Entertainment and Blue Underground. Its British DVD release was handled by Shameless Screen Entertainment. Blue Underground also released the film on Blu-ray.
All of the exterior scenes were filmed on location in New York City, which were the first scenes to be shot followed by interiors which were filmed in Rome, Italy. Some of the New York location shots were as follows:The opening scene with the old man walking his dog was shot near the edge of the southern bank of the East River between the Brooklyn and Manhattan Bridges in Main Street Park.
All of the bicycle girl scenes of her riding her bicycle down 5th Avenue as well as the scenes at Battery Park and on one ship of the Staten Island Ferry and the interior of ferry's car park.
The Butler Library and the Low Memorial Library buildings figure prominently in the scene where Lieutenant Williams first arrives at the Columbia University campus to locate and consult with Professor Davis.
The entrance way that Lieutenant Williams and Professor Davis emerge from at Mount Sinai Hospital after visiting Fay in her patient room is located at 1184 5th Avenue.
The sculptural stone doorway that Fay returns to later to examine the chipping in the stonework left by the ripper's knife blade is located at 834 East 161st Street in the Bronx.
The elevated train stairway that Fay descends to the sidewalk is located near 849 Prospect Avenue in the Bronx. Adjacent to this address is the now defunct Prospect Theater (later renamed the Olympic Theater) which displayed the Slaughter in San Francisco marquee visible in the same scene.