Hutch calls the apartment one night and asks Guy to speak to Rosemary, telling her to meet him the following morning at 11:00 AM at the Time-Life Building. He does not say what he wants to discuss, and Guy remains highly skeptical. When Guy leaves Rosemary alone in bed, she folds over in pain. The next day, she sets out to meet Hutch, still wracked by spasms of pain, having to pause in front of Radio City Music Hall. When Hutch does not show, Rosemary uses a pay phone to call him at home, and an unfamiliar woman answers, telling Rosemary that Hutch took ill that morning and has fallen into a deep coma. The woman identifies herself a Grace Cardiff, a friend of Hutch, and tells Rosemary there is nothing she can do to help.
By chance, Rosemary sees Minnie out shopping on the sidewalk, who tells Rosemary how faint she looks, and ushers her back home to The Bramford. Weeks later, at a small New Year's Eve party in the Castevets' apartment, Rosemary sits doubled over in pain in front of the TV, which is showing an old Hollywood musical. Dr. Sapirstein is there, and coldly tells Rosemary her pain will disappear "any day now," despite the fact that she describes it as like, "a wire getting tighter and tighter," inside her. Minnie introduces a dentist named Dr. Shand to Rosemary, saying he's the man who made the chain for her Tannis charm. As the clock tolls midnight, a party-hat-wearing Roman makes a peculiar toast: "To 1966—The Year One!"
In her kitchen, Rosemary eats a raw, bloody chicken heart, and catches her reflection in the side of the toaster. She rushes to the sink to rinse off her mouth and fingers. Guy later finds her in the kitchen, planning a meal for a party she wants to throw a week from Saturday. She insists they should only invite their young friends—no Minnie, Roman, Laura-Louise, or Dr. Sapirstein. Guy wonders whether Rosemary should consult Dr. Sapirstein further about her pain before taking on the labor of entertaining, to which Rosemary drolly replies, "Haven't you heard? It'll go away in a day or two."
Minnie, bringing over her daily vitamin mixture, sees Rosemary's party preparations and offers to help. Rosemary gently declines her aid, and tells her she won't be taking the mixture right away that day. Minnie cautions her against letting it sit, and offers to wait until Rosemary takes it, but Rosemary is able to guide Minnie gently out of the apartment, and then pours the drink down the drain. At Rosemary's party, music plays and a crowd of young, glamorous guests are gathered around discussing the Trench sisters, Adrian Marcato, and the mythology of The Bramford. Another topic of conversation is the sudden blindness of Donald Baumgart, the actor whom Guy replaced in rehearsals of a current theatrical production. Rosemary's friend Elise tells her she looks tired and asks her about Dr. Hill, but Rosemary tells her she is now seeing Dr. Sapirstein.
While arranging flowers, Rosemary becomes so weak she nearly faints, and Elise ushers her into the kitchen to look after her along with a few other close female friends. Rosemary's admission that she has been in pain since November shocks the women, and when Guy tries to enter the kitchen, they close him out. Elise tells her that experiencing such sharp pain must mean something is wrong, and that she should get a second opinion from Dr. Hill. After the party, Rosemary and Guy quarrel. Guy seems embarrassed that Rosemary caused a scene, and refuses to allow Rosemary get a second opinion on the grounds that it "wouldn't be fair to Dr. Sapirstein." Rosemary admits she stopped taking Minnie's vitamin drinks, when suddenly, mid-argument, Rosemary's pain stops. She begins to gasp and giggle and tells Guy she can feel the baby move. Gripping her stomach, she collapses into a chair out of joy and relief.
Rosemary resumes taking Minnie's vitamin drinks, and a montage shows the couple moving furniture into and readying a nursery. Three weeks before her due date, while packing her "hospital" suitcase, Rosemary receives a phone call from Grace Cardiff. She learns Hutch has died. At the funeral, Rosemary makes conversation with Hutch's children, until Grace herself pulls Rosemary aside. She hands Rosemary a book that Hutch mentioned in his final moments of delirium before succumbing to a fatal coma. Grace also tells Rosemary that Hutch had a message for her: "The name is an anagram."
Back at The Bramford, Minnie administers yet another drink to Rosemary and inspects her mail, turning over the package that contains Hutch's book suspiciously in her hands. She says she recognizes the return address and has been there many times. Rosemary bids her goodbye and unwraps the package, which contains a small leather-bound book called "All of them witches." Rosemary leafs through it, seeing underlined passages about something called the "Devil's Pepper"-- a fungus with a foul, pungent odor apparently used in witchcraft rituals. She lingers on pages showing an illustration and brief history of Adrian Marcato, which Rosemary begins to read aloud. She learns Adrian Marcato was killed outside The Bramford, not in the lobby like Hutch told her, and questions her own belief in witchcraft.
Pondering Grace's parting words, Rosemary takes out a Scrabble set, rearranging the letters "All of them witches," into "Comes with the fall," "Elf shot lame witch," and "How is hell fact me," the last one requiring her to keep a 'T' piece in her hand, but which moves her to remark, "Now that really makes sense." About to throw in the towel, Rosemary suddenly flips the book open again and turns to the pages about Adrian Marcato. She finds a photograph with a caption listing Adrian with his son, Steven. Rosemary lays out the letters "Steven Marcato" and realizes they rearrange perfectly as "Roman Castevet."
After Donald Baumgart, Hutch is the coven's next victim. The film generates an atmosphere of suspense and foreboding by strongly suggesting that Hutch is about to warn Rosemary before being unexpectedly incapacitated. His missing glove, a seemingly minor detail in the previous scene, is in fact what enables the coven to target him. Virtually the only character in the film not related to the coven, Hutch later arms Rosemary with information from beyond the grave in the form of a book—one of the two things Dr. Sapirstein told Rosemary never to consult.
The shot of Rosemary watching a Busby Berkeley-style musical on the Castevets' television again hints that her surroundings are merely a staged performance for her benefit. The Castevets' mild-mannered, old-fashioned New Year's Eve party is in fact a piece of carefully constructed scenery, where the guests have been instructed not to bring up the plot around Rosemary. Epitomizing the film's running themes of religion as performance, glamorous evil, and hiding in plain sight, the entire party is composed of coven members who perform for Rosemary, and whom she greets under the guise of socializing.
Dr. Sapirstein obscures Rosemary's sense of reality further by acting perfectly unconcerned by her reports of sharp pain. She describes it as "a wire getting tighter and tighter," a reference to her bound state, both literally during the rape and figuratively throughout her pregnancy. The "wire getting tighter" is at once a description of physical pain and a symbol for the coven plot slowly closing in on Rosemary. Roman's suggestive toast—"To 1966, The Year One!"-- is an ironic climax to the scene, essentially betraying the coven's presence in front of Rosemary, who has no context in which to understand it. (By now, we know Rosemary's due date is in June, 1966: or, 6/66.)
Sensing herself coming apart but not willing to give up entirely, Rosemary's decision to throw a party is the next major way she asserts her autonomy after cutting her hair. Guy is resistant and tells her to check with Dr. Sapirstein, whom he knows will discourage the idea, but Rosemary soldiers forward, exploiting the irony of the fact that her pain is going unacknowledged. The party sequence highlights the disparities between male-female and female-female bonds. Rosemary's friend Elise tends to her after she collapses while arranging roses, the film's symbol for Rosemary's womanhood and motherhood. The kitchen scene, in which a group of women listen to Rosemary's account, is the only scene in the film comprised entirely of women unrelated to the coven, and they critically shut Guy out of the room. Social norms around female intimacy (e.g. discussing a pregnancy with one's friends—the second thing Dr. Sapirstein told Rosemary never to do) express the conventions of Gothic narrative in which a female protagonist must battle to perceive the world from within an ambiguously evil, male-dominated power structure.
The name of Hutch's book—"All of them witches"—doubles as the solution to the film's mystery. They are all witches, everyone around Rosemary: Guy, Minnie, Roman, Dr. Sapirstein, Dr. Shand, Laura-Louise, and countless others. The film's use of anagrams is another metaphor for hiding in plain sight: the letters and evidence are there, and merely need the proper context or arrangement to be understood. Rosemary's revelation that 'Roman Castevet' is an anagram for 'Steven Marcato' marks a turning point in the film's plot, finally cluing her into the coven's presence and history.