As the film opens, Barbara Scott is performing oral sex on her husband Chris in their bedroom with the lights out. Chris turns the lamp on so that he can watch her do it. She stops to turn it off again, then resumes. They have an argument about having sex with the lights on or off, and Chris eventually does have sex with her, but she's clearly not happy about doing it with the lights on. After she comes back from cleaning up in the bathroom, she finds him getting dressed and packing a bag. He informs her that he's had it with her repressed behavior. Barbara guesses that he's really leaving her and their son Paul to shack up with his much younger secretary.
That morning, Barbara explains to Paul that this has been coming for a long time. While Paul thinks that his father will eventually come back, she tells him to forget it. When told that he has to choose which of his parents to live with, Paul immediately chooses his mother, and offers to quit school and get a job. Barbara rejects the notion, and states that she'll get a job, since she's not "over the hill". Staring at her semi-exposed breasts, Paul agrees. She is embarrassed but thanks him for the compliment.
Sometime later, Barbara steps into a phone booth to call her friend Gina, who takes the call while still in bed with a pair of lovers, one male and one female. Barbara tells Gina about Chris leaving her, and Gina agrees to meet her later. After hanging up, Gina begins to make love to her lovers. Meanwhile, Barbara scans the want ads and checks out a store with a help wanted sign. She seems very depressed as she walks down a street.
Meeting Gina at a dockside restaurant, Barbara complains about her husband. Gina suggests that what Barbara needs is a new guy, and offers to find her one. Barbara declines, saying that she needs more time. But Gina insists, stating that she knows the perfect guy for Barbara. She then asks about the job hunting. Barbara isn't having much luck, due to her age. Gina then reminds Barbara about Jerry Morgan, an old friend of Barbara and Chris, who has an office not far from their home. She then asks, very suggestively, about Barbara's son.
Paul is being quizzed about historical facts by his girlfriend, Sherry, though he'd much rather make out, and starts kissing her thighs (and implicitly performing oral sex on her.) After he answers all her questions correctly, Sherry rewards Paul by performing oral sex on him. A friend of theirs, Diane, walks in on them and admires Paul's erection before starting to leave. Sherry offers to share, and they both perform oral sex on Paul. In a magical dissolve, all three become naked. Paul wants to have sex with Sherry, but she tells him to do it with Diane first, as Diane has apparently never experienced orgasm.
Some time later, Barbara returns home and finds a pair of panties on the couch. She asks Paul about his father, and Paul confirms that he's decided staying with her. She's pleased by this, and tries to kiss him on the cheek, but Paul turns at the last moment so that they're kissing on the lips. The kiss is a rather passionate one, to Barbara's surprise. Paul repeats his offer to quit school, but Barbara reveals that she's found a job with Jerry, noting that she doesn't think he really needs the help.
The next day, Barbara is typing in Jerry's office, under his watchful supervision. She's obviously not very good at it. Gina, being carressed by her two lovers, calls to ask Barbara whether Charlie called and whether Barbara will go out with him. Barbara answers yes to both questions, but she is concerned about Charlie's intentions. While Gina assures her that Charlie's a pussycat, Jerry interrupts to ask Barbara if she can take an important letter for him. But rather than dictate a letter, he begins to carress Barbara over her protests, while Gina listens over the phone and wonders what's going on. Barbara storms out of the office, only to come back and demand that she be paid for her time before she quits. Jerry apologizes for his actions and confesses that he's always been very attracted to her. He begs her to reconsider quitting, and she agrees ... despite a rather crude joke from Jerry about how she'll get a pay cut for refusing his advances.
Gina, enormously aroused by the thought of her best friend being sexually assaulted, has her lovers perform oral sex on her, before doing so herself to her female lover. She then has her lovers have sex with each other, and then has sex with her male lover.
Paul and Sherry arrive at Paul's home, and Paul tells Sherry to wait while he sees if his mother is home. She waits, but masturbates while doing so. Barbara is in the shower, and Paul watches her from concealment, rubbing his erection through his jeans as he does. He continues to watch as she does her make-up and dresses, then flees to the living room. When Barbara comes out, she announces that she has a date, and leaves Paul and Sherry to their own devices. Paul licks Sherry's breasts and fingers her vagina before performing oral sex on her.
Meanwhile, Barbara's date with Charlie has started poorly, as she clearly finds him repugnant. Both of them have been misinformed about the other by Gina.
Sherry and Paul are performing oral sex on each other, and then have sex with each other. After the climax, she is surprised by his ardor, which is revealed to be due to his memories of his voyeurism on his mother. They begin to do it again.
Charlie has taken Barbara to a swinger's party, much to her consternation. She refuses to participate, and he finds another partner. Barbara observes a variety of sex acts, including a daisy chain, lesbianism, and a number of threesomes. Another man, whom she states is young enough to be her son, comes onto her, and she rejects his vigorous attentions. When it's over, Charlie drives her home, and offers to take her out again. She tells him not to bother.
Despite herself, Barbara finds herself fantasizing about what it would have been like to take part in the orgy, and becomes very aroused. Unable to find relief through masturbation, and discovering that she's out of sleeping pills, she gets up and wanders the hall in her nightgown. She passes Paul's room, hears him make a noise and looks in on him, but discovers that he's sleeping in the nude. While she turns to go, she starts to fantasize about the orgy again, and turns back to begin rubbing Paul's penis, and then performs oral sex on him. This wakes him up, and they have sex.
The next day, Paul wakes up alone. He pulls on his jeans and heads out to the kitchen, where he finds a remorseful note from his mother who tells him that they'll talk about what happened that night. Paul doesn't seem bothered about any of this.
In contrast, Barbara is horribly upset, unable to work. Gina calls her, and Barbara tells her about the bad date with Charlie before hanging up. Jerry asks her what is the matter, and then offers to take the rest of the day off with her. They have a very nice date, taking in the sights of San Francisco.
When Jerry drives her home, he offers to come in with her, but Barbara declines. She does offer to have supper with her and Paul tomorrow. She goes in to find Paul waiting for her in her bed, asking why she's kept her lover waiting. Despite Barbara's half-hearted attempts to talk seriously about it, she is seduced into having sex with Paul again.
The next day, Gina is with her lovers when Barbara, in desperate need of advice, drops by for a visit. After some confused utterances, Barbara confesses that she's had sex with Paul. Gina finds this to be incredibly arousing, and rubs herself to an orgasm listening to Barbara's explanation. Finding Gina to be no help, Barbara leaves.
That night, Jerry can be found swimming in the pool behind Barbara's house, when Barbara comes out to tell him that supper is ready. He makes another pass at her, which she declines on the grounds that Paul could be watching. The three of them have dinner together, and Jerry invites Paul and Barbara up to his cabin at Lake Tahoe. Paul declines and heads off in a bad mood, stating that he's lost his appetite. Jerry proceeds to literally carry Barbara off to the bedroom, and they perform oral sex on each other. Jerry proposes marriage, but Barbara asks him not to rush her. She intends to live her life for herself, and part of her life will be keeping him as a lover. But there's another part, and when he asks her about that, she just presses her finger to his lips and shushes him. (Implicitly, she's going to continue having sex with Paul as well ...)