During a long and vivid nightmare, thirty-nine-year-old Joan Mitchell (Jan White) is tormented by her fear of aging and the neglectfulness of her work-obsessed husband, Jack (Bill Thunhurst). In her dream, a real estate agent tries to sell her on the amenities of her large home and affluent lifestyle. Introducing her to a virile, young man he calls Billy, the agent urges her to try him. When Joan awakens, Jack, who is preparing to leave on a business trip, kisses the air near her cheek and tells, her to have a good day. Later, while discussing the dream with her condescending psychologist, Dr. Miller (Neil Fisher), Joan is told that she has only herself to blame for her feelings of imprisonment. Joan is shown food shopping at a local market, dropping off her husband's suit at a local dry cleaners, getting her car washed at a local car wash, as well as cleaning house.At a cocktail party, Joan's confidante, Shirley Randolph (Ann Muffley), relates to Joan and several of their female friends that she has met a woman who is a witch. Before falling asleep that night, Jack, who has no sense of Joan's anguish, boasts that they are doing well. As it begins to storm, Joan drifts into a nightmare in which she sees hands rising from the side of the bed and awakens to find Jack seated on the floor doing sit-ups.The next morning, Joan's nineteen-year-old daughter Nikki (Joedda McClain) surprises Joan by remarking that she looks good and has a great body. Later, the usually repressed Joan enjoys lying naked in bed as well as looking at her nude body in the bathroom mirror.That evening, Joan picks up Shirley where the Catholic-reared Joan confesses that she feels guilty for fantasizing about having an affair. They drive to a local house where Shirley introduces Joan to Marion Hamilton (Virginia Greenwald), a second-generation witch who otherwise lives a lifestyle much like theirs. Although she is too frightened to have her tarot cards read, Joan peruses a book about witchcraft while Marion reads Shirley's cards, and she listens thoughtfully as Marion discusses how former secrets of the craft are now available in books. Afterward, while driving back home, Joan admits to Shirley that she is intrigued by witchcraft, but believes that treating it like another fad undermines what it has to offer.Joan and Shirley return to the Mitchell house, where Nikki is entertaining Gregg Williamson (Raymond Laine), a friend from college whom Joan recognizes as Billy in her dream. When Gregg claims he recognizes Joan, they soon establish that they had participated in the same volunteer community clean-up project. After Joan offers everyone drinks, Shirley, troubled by marital problems, gets inebriated and blurts out that Joan wants to be a witch. A discussion ensues, during which Gregg, an arrogant student teacher of sociology, claims that the occult seems real to people who are manipulated by the power of suggestion. To prove his point to Joan, he alters a cigarette to look like a hand-rolled joint of marijuana and offers it to the unwitting, but curious Shirley, who soon believes she is high. At Gregg's cruel prodding, Shirley hysterically voices her anxieties about getting older. Joan and Nikki silence Gregg, who offers an apology, but noting his insincerity, Joan tells him to leave. Before heading for the door, Gregg further angers Joan by saying that she is interested in him sexually. Nikki apologizes to Joan and admits that her relationship with Gregg is not serious. Afraid to face her husband alone in her present state, Shirley asks Joan to spend the night at her house.After informing Nikki of her plans, Joan drives Shirley home, but during the drive, Shirley angrily accuses her of forming opinions about experiences she has never had. Offended, Joan leaves Shirley at her door and returns home. Sensing that Gregg and Nikki are there having sex, Joan slips discreetly into her own room, where she buries her head under a pillow to block the sounds of a storm and their exuberant copulation, and struggles with her own sexual urges. Realizing that Joan has returned home, Nikki enters her room and accuses her of violating her privacy.In the morning, Joan discovers that Nikki has run away. During a therapy session, Miller brushes aside Joan's anxieties about Nikki's welfare, but enthusiastically pronounces a breakthrough when Joan cries about her personal worries. When Jack learns about Nikki's departure, he is more concerned that she might get pregnant and slaps Joan several times for not interrupting their daughter's tryst. Two policemen investigating Nikki's disappearance question the Mitchells about their acquaintances, but Joan is careful not to implicate Gregg.When Jack goes away on a two-week business trip, Joan temporarily dismisses the housekeeper so that she can be alone. After getting dressed up, Joan visits Gregg at the university to ask him where Nikki is staying. Claiming not to know, Gregg states that just because they had sex does not mean they are having a relationship. Again, he accuses Joan of desiring him and adds that he is available.Some time later, after Jack has returned from his business trip, Joan dreams that someone is trying to break the chain on the door. She grabs a kitchen knife, but a grotesquely masked man (Bill Hinzeman) knocks it from her hands and chases her. In her bedroom, as he rapes her, she pulls off his mask, but then wakens to learn that she has disturbed Jack's sleep.During Jack's next business trip, Joan creates an altar on her living room coffee table and begins to experiment with spell-casting, which she has learned from a book that she purchases during an excursion to Antic Row in downtown Pittsburgh which is titled 'How to Become a Witch; A Primer'. After performing a conjuration, Joan waits for something to happen, but when nothing does, she calls and invites Gregg to come over to have sex. Soon after, Joan asks to join Marion's coven, saying that she believes in the power of witchcraft, as she has already "made things happen." Marion agrees to consider her request, but warns her not to abuse the power.Joan then has another nightmare, similar to the last, in which a masked man again breaks the chain on the door and chases her through the house, but she is awakened by a call from the police, who have found Nikki. Slightly drunk, Joan is feeling vulnerable when she again invites Gregg over for sex. When she tells him she is a witch, he calls her a hypocrite. Insisting that the only thing they are doing is balling, he initiates rough sex. Afterward, as he lies naked, she begins a ritual in which she summons the spirit Virago, which enters the house through a utility room window as a cat. As it approaches the living room unnoticed, Gregg grabs Joan for an even wilder session of sex. After they are finished, Joan says that this was their last time, as Nikki will be returning in a few days after she was told by the police over the phone that Nikki is in Buffalo and will be returning.During the night, in another dream, Joan goes about her chores, happily awaiting the return of Nikki. She is pleased when she hears a car approaching, but is struck with terror when she realizes that the masked man is trying to break in. She runs to the basement, where she finds her husband's rifle and bullets. Jack, returning late in the night from his business trip, finds the door to the house chained. Cursing, he tries to force it open, and Joan shoots him dead. Although suspicious, the investigating policemen note that Jack was not expected to return from his trip until the next day and that Joan can convincingly claim that she thought he was an intruder. For lack of evidence to support murder, they report his killing as accidental.Later, Joan undergoes a ceremonial initiation into Marion's coven, which culminates in a ritual flagellation. Months later, while attending a party of her housewife friends, the widowed Joan is asked by an amazed acquaintance why she seems so different. Joan states simply, "I'm a witch."