Antoinette's story begins when she is a young girl in early nineteenth- century Jamaica. The white daughter of ex-slave owners, she lives on a run-down plantation called Coulibri Estate. Five years have passed since her father, Mr. Cosway, reportedly drunk himself to death, his finances in ruins after the passage of the Emancipation Act of 1833, which freed black slaves and led to the demise of many white slave owners. Throughout Antoinette's childhood, hostility flares between the crumbling white aristocracy and the impoverished servants they employ.
As a young girl, Antoinette lives at Coulibri Estate with her widowed mother, Annette, her sickly younger brother, Pierre, and gossiping servants who seem particularly attuned to their employers' misfortune and social disrepute. Antoinette spends her days in isolation. Her mother, a beautiful young woman who is ostracized by the Jamaican elite, spends little time with her, choosing to pace listlessly on the house's glacis (the covered balcony) instead of nurturing her child. Antoinette's only companion, Tia, the daughter of a servant, turns against her unexpectedly.
One day, Antoinette is surprised to find a group of elegant visitors calling on her mother from Spanish Town, the island's version of a sophisticated metropolis. Among them is an English man named Mr. Mason who, after a short courtship, asks for Annette's hand in marriage. When Mr. Mason and Annette honeymoon in Trinidad, Antoinette and Pierre stay with their Aunt Cora in Spanish Town.
In the interim, Mr. Mason has had the estate repaired and restored to it to its former grandeur, and has bought new servants. Discontent, however, is rising among the freed blacks, who protest one night outside the house. Bearing torches, they accidentally set the house on fire, and Pierre is badly hurt. As the family flees the house, Antoinette runs desperately towards Tia and her mother. Tia throws a jagged rock at Antoinette, cutting her forehead and drawing blood.
The events of the night leave Antoinette dangerously ill for six weeks. She wakes to find herself in Aunt Cora's care. Pierre has died. Annette's madness, which has revealed itself gradually over the years, has fully surfaced after the trauma of the fire. When Antoinette visits her mother, who has been placed in the care of a black couple, she hardly recognizes the ghostlike figure she encounters. When Antoinette approaches, Annette violently flings her away.
Antoinette then enrolls in convent school along with other young Creole girls. For several years, she lives at the school with the nuns, learning everything from proper ladylike deportment to the tortured histories of female saints. Antoinette's family has all but deserted her: Aunt Cora has moved to England for a year, while Mr. Mason travels for months away from Jamaica, visiting only occasionally.
When Antoinette is seventeen, Mr. Mason announces on his visit that friends from England will be coming the following winter. He means to present Antoinette into society as a cultivated woman, fit for marriage. At this point, the end of Part One, Antoinette's narration becomes increasingly muddled, jumping from present- tense descriptions of her life in the convent to muddled recollections of past events.
Antoinette's husband, an Englishman who remains nameless, narrates Part Two. After a wedding ceremony in Spanish Town, he and Antoinette honeymoon on one of the Windward Islands, at an estate that once belonged to Antoinette's mother. He begins to have misgivings about the marriage as they approach a town ominously called Massacre. He knows little of his new wife, having agreed to marry her days before, when Mr. Mason's son, Richard Mason, offered him £30,000 if he proposed. Desperate for money, he agreed to the marriage.
When the couple arrives at Granbois, Antoinette's inherited estate, the man feels increasingly uncomfortable around the servants and his strange young wife. Hostility grows between the man and Christophine, Antoinette's surrogate mother and a servant who wields great power in the house. The man soon receives a menacing letter from Daniel Cosway, one of old Cosway's illegitimate children. Venomous in tone, letter warns of Antoinette's depravity, saying that she comes from a family of derelicts and has madness in her blood. After reading this letter, the man begins to detect signs of Antoinette's insanity.
Antoinette, sensing that her husband hates her, asks Christophine for a magic love potion. Christophine grudgingly agrees. That night, when the man confronts Antoinette about her past, they argue passionately. He awakes the next morning believing he has been poisoned, and he later sleeps with the servant girl, Amelie, who helps him recover. Sitting in the next room, Antoinette hears everything.
The next morning, Antoinette leaves for Christophine's. When she returns, she seems to be totally mad. Drunk and raving, she pleads with the man to stop calling her "Bertha," a name he has given her without explanation. Antoinette then bites her husband's arm, drawing blood. After she collapses and falls in bed, Christophine rails at him for his cruelty. That night, he decides to leave Jamaica with Antoinette.
Antoinette narrates Part Three from England, where she is locked away in a garret room in her husband's house, under the watch of a servant, Grace Poole. A hidden captive, Antoinette has no sense of time or place; she does not even believe she is in England when Grace tells her so. Violent and frenzied, Antoinette draws a knife on her stepbrother, Richard Mason, when he visits her. Later she has no memory of the incident. Antoinette has a recurring dream about taking Grace's keys and exploring the house's downstairs quarters. In this dream, she lights candles and sets the house ablaze. One night, she wakes from this dream and feels she must act on it. The novel ends with Antoinette holding a candle and walking down from her upstairs prison.