The novel opens a short while after the Slavery Abolition Act 1833 ended slavery in the British Empire on 1 August 1834. The protagonist Antoinette relates the story of her life from childhood to her arranged marriage to an unnamed Englishman (implied as Mr Rochester from Jane Eyre). As their marriage progresses, Antoinette, whom he renames "Bertha" and confines to a locked room, descends into madness, in part from despair at being torn from her island home in the Caribbean and subjected to an alien culture and climate.
The novel is split into three parts. Part One takes place in Coulibri, Jamaica and is narrated by Antoinette. Describing childhood experiences, she reviews several facets of her life, including her mother's mental instability and her mentally disabled brother's tragic death.
Part Two alternates between the points of view of her husband and of Antoinette during their 'honeymoon' excursion to Granbois, Dominica. Likely catalysts for Antoinette's downfall are the mutual suspicions that develop between the two and the machinations of Daniel, who claims he is Antoinette's (illegitimate) brother; he impugns Antoinette's reputation and mental state and demands hush money. Antoinette's old nurse Christophine openly distrusts the Englishman. His apparent belief in the destructive accounts about Antoinette aggravate the situation; he becomes visibly unfaithful to her. Antoinette's increased sense of paranoia and the bitter disappointment of her failing marriage unbalance her already precarious mental and emotional state.
Part Three is the shortest part of the novel; it is from the perspective of Antoinette, renamed by her husband as Bertha. She is largely confined to 'the attic' of Thornfield Hall, the Rochester mansion she calls the "Great House". The story traces her relationship with Grace, the servant who is tasked with guarding her, as well as her disintegrating life with the Englishman, as he hides her from the world. He makes empty promises to come to her more, but sees less of her. He ventures away to pursue relationships with other women—and eventually with the young governess, Jane Eyre. Expressing her thoughts in stream of consciousness, Antoinette/Bertha decides to take her own life as she believes this is her destiny.