Sensual images of a couple, a man and a woman, making love in the shower. He (Robbie L. McDermott) suddenly attacks her.
Cut to a couple making love in bed. It looks like she was the woman who was remembering the shower scene. When he finishes, she doesn't seem to be much satisfied. The radio is on.
The woman is named Kate Miller (Angie Dickinson). She tells off her son Peter "Pete" Miller (Keith Gordon) because he doesn't want to go to the museum with her: he prefers to stay home working on an improved computer which can count binary numbers up to 20 digits. It looks like Kate's partner, Mike (Fred Weber) is not Pete's father.
Kate leaves home to see her psychiatrist, Doctor Robert Elliott (Michael Caine), who has to perform the duties of receptionist as Mary is on a holiday. Kate complains about the "surprise" visit of her mother from Florida due to her approaching birthday. She also complains about Mike's "specialties". She is fed up with her husband and mother, but she doesn't say anything to the right person. Elliott tells her not to get angry with him but with Mike and tell him that he's bad in bed. She questions Elliott whether he finds her attractive or not. He admits that he finds her attractive but he also says that he's married and doesn't want to put his marriage in danger. Kate says she isn't sure whether putting his own marriage with Mike at risk would be worthwhile.
Later, Kate is at the museum. A man sits next to her. She leaves a glove for him. They follow each other around the museum. She loses his sight, so she has an expression which says "obviously, he wasn't serious about me", but when he turns around he's there, staring at him. She seems to panick for a second and then is happy that he's not there. But he appears again, on her back, touching her with her own glove. When she realises she's lost it, she tries to find it, and then she realises he's got it. Music in innuendo while she tries to find him. When she leaves the museum, she sees his hand showing the glove from a yellow cab. She smiles and tells him politely "thank you for retrieving my missing glove", but he pulls her inside. They make love while the taxi driver (Sean O'Rinn) looks at them through the inside mirror. She has a noisy orgasm.
They arrive to his destination, his apartment. She stays with him through the afternoon. When she is about to leave, she finds papers stating that he's suffering from a sexually-transmitted disease, and that she will have probably caught it. She leaves. When she is in the lift, she is so nervous that she caresses her hands one against the other. Then, she realises that she's forgotten her wedding ring in the apartment of the man. She has to go to the flat again, but when she gets to the right floor, another blond woman - probably using a wig - with dark sunglasses stabs her with a straight razor. Kate is left for dead, all bloodied. Another couple of people has called the lift: they are discussing the convenience of buying the shares of a particular company. He runs away, but Elizabeth "Liz" Blake (Nancy Allen) stares at him. When she looks inside the lift, Kate is still alive. They try to reach out for each other's hand, while the doors of the lift are slowly closing down. In the last second, Liz stares up and in the reflection of the mirror she sees the blonde-wigged woman who is about to cut her hand as well. She backs up. A cleaning lady (Amalie Collier) appears, and she shouts when she looks at Liz with the razor menacingly held by her hand.
Elliott finds an answering machine left for a man (William Finlay) saying that there is a woman trying to het out of his body. He's worried, because the man has also admitted to stealing a straight razor from the cabinet of his office.
Detective Marino (Dennis Franz) questions Elliott, who gets very defensive but doesn't mention the answering machine message. Meanwhile, Liz is waiting to be questioned as well and Pete is listening to the whole conversation. Marino mentions that the man, Warren Lockman (Ken Baker) was recognised by the taxi driver. Mike picks Pete up.
Marino questions Liz about what she was doing in the building. She says she was with a married man. She is a prostitute. Marino suspects of her: nobody saw the blonde woman and her fingerprints are on the weapon. The man, Ted (Norman Evans), is from out of the city, and Marino tells Liz that she is the only interested person in finding Ted.
When Liz leaves, Pete is also stuck with a man he doesn't love at all - his true father died during the 'Nam war. He tries to investigate the case as well. In his blue moped, he follows Liz all over the city. He arranges a camera to be hidden inside the box at the back of the bike. While he watches Liz, the mysterious man has phoned Elliott again, threatening her. Liz tries to stay home, but she needs the money to invest in the company which Ted had recommended, so she asks for 500 dollars to meet a client, Cleveland Sam (Brandon Maggart), in the room 331. She leaves a bit distraught. She jumps onto a taxi but realises that somebody is following her. She asks the young taxi driver (Bill Randolph) to lose the follower. The taxi driver wants to meet her for dinner. The taxi driver tries to help Liz: she opens the door of the taxi when the blonde lady is following Liz. Liz runs to the underground, but when she tries to leave another blonde transsexual or travesty scares her off. Liz approaches some black men (Robert Lee Rush, Anthony Boyd Scriven, Robert McDuffie and Frederick Sanders) who are listening to the radio, but one of them, called Sonny, threatens her as the train arrives.
Liz tells the police officer (Samm-Art Williams), who ends up thinking she is making it all up, because he can't see any gang threatening to "cut her up", and Liz's claims that a blonde is following her leave the officer even more convinced that she's mad. In the next station, the police officer leaves. When the doors close, the gang appears again, just causing a nuisance to all passengers. Liz runs from them and closes one door behind. At that moment, the blonde woman puts a hand on her mouth and wants to slash her with another straight razor. Fortunately, Pete saves Liz using an anti-rape spray of his invention. Liz invites him over. Pete sleeps at Liz's, and she promises that he won't tell anyone that he's not studying French with at his friend Paul's. Liz tells him that she knows that the blonde woman left the doctor's office, but she can't explain how she knows it. As Marino can't get a register order like that, he suggests her to enter Elliott's office and check the doctor's agenda.
Dr. Levy (David Margulies) tells Elliott that one of her patients Bobby / Bobbi (William Finlay) has stopped seeing him because he didn't approve of his sex change. Elliott tells Levy that Bobbi must be the murderer of the lady in the lift, and they also comment on the missing razor. Later, Liz pretends to be a new patient of dr Elliott. She tells him about an erotic dream of her, but also admits that she's a prostitute, although she sometimes makes love to men for pleasure. She gets naked trying to seduce him. During all this time, Pete is watching with some lens. Liz checks the address book of dr Elliott and she thinks that the name she's looking for is Chris Clemens. Pete tries to to tell her that the blonde woman is inside the office - he's seen it - but a blonde woman has attacked him, so when he finally can cry out to Liz the blonde woman is already prepared to slash her with a Straight Razor.
At that moment, the blonde woman who is holding Pete down shoots Bobbi.
The wig falls off. The blonde woman is a wounded man. It's the doctor Robert Elliott.
Some time later, Levy, Marino, Pete and Liz are sitting down. Levy explains that Elliott had a double personality: he was the masculine doctor but he was also a patient who wanted to have a sex change performed, and giving Bobbi as his name, he visited doctor Levy. Levy says that Elliott represent Bobbi, but that when Bobbi decided to go for the sex change surgery, that pushed him to act. Levy said that every time that doctor Elliott felt attracted by a woman her alter-ego killed that woman. The blonde woman who attacked Pete was police officer Betty Luke (Susanna Clemm), who was in charge of following Liz. Marino pushed her to enter dr Elliott's address book because he didn't have any proofs against him.
Liz explains to Pete how a sex change operation takes place. He replies, sitting confortably at a restaurant with her, that he may change the subject of his investigation, and use himself as the subject of that sex change, instead of investigating about computers.
Meanwhile, back at a madhouse, a nurse (Anneka di Lorenzo) walks in to give Dr Elliott the medicine he must take. He looks defenseless and sleepy, but he jumps and strangles her. All the loose madmen cheer. Pete invites her to sleep at his home, saying that his step-father won't mind.
Naked in the shower, Liz feels some danger. Somebody dressed as a nurse approaches, and she knows it. She doesn't have anything to defend herself in the bathroom, except for something in the medicine cabinet. However, suddenly, the razor is at Liz's neck. The same blonde woman cuts Liz's neck.
Terrified, Liz wakes up in a bedroom at Pete's. He tries to calm her down.
FADE TO BLACK