Marian Leatherby, the 92-year-old narrator, lives in a Latin American city with her son Galahad, a low-ranking consular employee, and his family. Nearly deaf and bent by rheumatism, Marian occupies a back room she shares with two cats, a red hen, and the family's maid. She longs to visit Lapland, where she dreams of riding in a sledge drawn by woolly dogs.
One Monday, her friend Carmella presents Marian with a hearing trumpet encrusted with silver and mother-of-pearl. Carmella advises her to keep it secret. That evening, Marian hides in the hallway and overhears Galahad, his wife Muriel, and their son Robert discussing plans to send her to an institution. Robert calls her a "drooling sack of decomposing flesh" (13) and wants her room for a motorcycle workshop. Muriel describes a place in Santa Brigida run by a religious group called the Well of Light Brotherhood. Devastated, Marian tells Carmella, who launches into impractical rescue fantasies. When Galahad presents the move as a "nice holiday," Marian refuses to be deceived and packs her trunk as though preparing for Lapland.
Lightsome Hall is nothing like the prison Marian expected. Behind high walls, she finds a castle with courtyards, gardens, and bizarre pavilions shaped like toadstools, a boot, and a circus tent. She is assigned to a whitewashed tower called the Lookout.
Dr. Gambit, the director, presides over meals with speeches on "Inner Christianity" and "Self Remembering," a pseudo-spiritual doctrine. His wife supervises daily chores with an agonized smile. Marian's companions, all women over 70, include Georgina Sykes, who becomes Marian's closest friend; Natacha Gonzalez, prone to visions and claims of psychic power; Vera Van Tocht, devoted to Natacha; Maude Somers, a timid seamstress; the Marquise Claude la Checherelle; Veronica Adams, a 98-year-old blind painter; Christabel Burns, a Jamaican woman who carries covered trays to the castle tower; and Anna Wertz.
An oil painting in the dining room captivates Marian: It depicts a nun with a malicious face who appears to perpetually wink. Marian names her Doña Rosalinda Alvarez della Cueva and imagines her as the abbess of El Convento de Santa Barbara de Tartarus. Dr. Gambit lectures Marian about her "interior impurities," advising her to give up cauliflower.
Events darken during a cooking class. Through the kitchen window, Marian watches Natacha drill holes in chocolate fudge, fill them with what appears to be rat poison, and hide the pieces in her igloo bungalow while Mrs. Van Tocht stands watch. Marian sees Maude slip in and steal the fudge. When Natacha approaches Georgina proposing a reconciliation feast with fudge, Marian realizes Georgina was the intended victim but does not intervene.
Christabel gives Marian a leather-bound book containing the life of Doña Rosalinda. The account tells how Rosalinda entered the convent around 1710, using piety as a front for occult ambitions. She sought a powerful ointment called Musc de Madelaine, found in Nineveh, that produced levitation when inhaled. The Bishop of Trève les Frêles stole the ointment for her. He later reported that the Knights Templar possessed the Holy Grail in Ireland, described as the chalice of the Goddess Venus. The Abbess traveled there in disguise and entered the vault containing the Grail but was forced to return it. Back in Spain, her body swelled and exploded. From the fumes emerged a luminous, winged boy called Sephira. The nuns proclaimed a miracle, and the Abbess was canonized in 1756.
Maude dies during the night. Marian connects the death to the stolen fudge and feels guilty for not intervening. Peering through the skylight of Maude's bungalow, Marian and Anna discover that the corpse is that of an elderly man. Georgina explains that Maude was really Arthur Somers, whom Georgina had known in New York. Arthur fell in love with Veronica Adams and retired to the institution as Maude.
Marian and Georgina report the murder to Dr. Gambit, who dismisses their account as "diseased imagination." They stop eating institutional food. Carmella visits and proposes a hunger strike: The residents should refuse all food, survive on chocolate biscuits, and demand the expulsion of Natacha and Mrs. Van Tocht. That night, the residents gather at the bee pond. Christabel plays a tom-tom and chants an invocation to Hekate, an ancient goddess, addressing her as "High Queen of Tartarus." A cloud takes the shape of an enormous bumble bee wearing an iron crown, resembling the Abbess, before fading and leaving a scent of wild honey.
The hunger strike proceeds amid inexplicably bitter cold, with snow appearing in a tropical country. Carmella returns, now fabulously wealthy after discovering a uranium mine in her back yard. She arrives in a lilac limousine driven by a Chinese chauffeur named Majong and threatens Dr. Gambit with press exposure. Natacha and Mrs. Van Tocht depart.
Christabel poses three riddles about the tower's mysterious prisoner: The first describes the Earth, the second the Pole Star, and the third concerns Sephira. The sun fails to rise. Carmella returns with supplies, including sheepskin cloaks and 12 cats. Using a planisphere, a star-charting disk, the group confirms the Earth has shifted on its axis. An earthquake cracks the castle tower, releasing Sephira, a luminous six-winged creature, who flies north.
Christabel leads Marian to the cracked tower and offers a choice: up or down. Marian descends alone into a chamber where fire burns from a cavity in the floor. Beside it sits a woman stirring an iron cauldron: Marian herself, but less bent, more vital, and ageless. This double calls the place the "Womb of the World" and instructs Marian to jump into the boiling soup. Marian leaps in and finds herself standing outside the pot, stirring the broth in which her own body boils. In an obsidian mirror, she sees three faces winking alternately: the Abbess, the Queen Bee, and her own.
Marian emerges rejuvenated. The institution has collapsed, presumably burying the Gambits. Her companions reveal they have all undergone the same ritual. They settle in the warm underground chamber, cultivating mushrooms and keeping goats.
Marian's old friend Marlborough arrives in a gilded, atom-propelled Ark mounted on runners, accompanied by wolves. His sister Anubeth, a wolf-headed werewolf, has married the pack's leader. An immortal postman named Taliessin brings news that the planet is devastated and that the Templars' fortress in Ireland exploded, tossing the Holy Grail free. He declares the Great Mother Goddess cannot return until the Cup is restored.
Christabel performs a ritual, and millions of bees form the figure of the Goddess, who instructs the group to follow the swarm. They set out: bees, wolves, seven old women, Taliessin, Majong, Marlborough, Anubeth, and the Ark. The Marquise commands the strategy: Wolves surround the Archbishop's palace, and when the door opens, the swarm carries out the Grail, leaving a trail of honey on the snow.
The group returns to the cavern to live among cats, wolves, bees, and goats. According to the planisphere, their location now corresponds to where Lapland used to be. A she-wolf gives birth to white woolly puppies, and the group plans to train them to draw a sledge. Marian closes her account: "If the old woman can't go to Lapland, then Lapland must come to the Old Woman."