Margaret Hale, 19, happily returns home from London to the idyllic southern village of Helstone after her cousin Edith marries Captain Lennox. She lived nearly 10 years in the city with Edith and wealthy Aunt Shaw to learn to be an accomplished young lady. Margaret, herself, has refused a marriage offer from the captain's brother, Henry, a rising barrister. But her life is turned upside down when her father, the pastor, leaves the Church of England and the rectory of Helstone as a matter of conscience—his intellectual honesty having made him a dissenter. On the suggestion of his old friend from Oxford, Mr. Bell, he settles with his wife and daughter in Milton-Northern, where Mr. Bell was born and owns property. An industrial town in Darkshire, a textile-producing region, it is engaged in cotton-manufacturing and is smack in the middle of the industrial revolution where masters and workers clash in the first organised strikes.
Margaret finds the bustling, smoky town of Milton harsh and strange and she is upset by the poverty all around. Mr. Hale, in reduced financial circumstances, works as a tutor and counts as his pupil the rich and influential manufacturer, Mr. John Thornton, master of Marlborough Mills. From the outset, Margaret and Thornton are at odds with each other: She sees him as coarse and unfeeling; he sees her as haughty. But he is attracted to her beauty and self-assurance and she begins to admire how he has lifted himself from poverty.
During the 18 months she spends in Milton, Margaret gradually learns to appreciate the city and its hard-working people, especially Nicholas Higgins, a Workers' Union representative, and his daughter Bessy with whom she develops a friendship. Bessy is consumptive from inhalation of cotton dust and she eventually dies from it. Meantime, Margaret's mother is growing more seriously ill and a workers' strike is brewing.
Masters and hands (workers) do not reach a resolution on the strike and an incensed mob of workers threatens Thornton and his factory with violence after he brought Irish workers into his mill. Margaret implores Thornton to intervene and talk to the mob but he manages merely to fuel their anger. Margaret intervenes too and is struck down by a stone. Soldiers arrive, the mob disperses and Thornton carries Margaret indoors, professing his love to her unconscious prostrate figure.
Thornton proposes; Margaret declines, wholly unprepared for his declarations of love and offended by assumptions that her action in front of the mob meant she cared for him. Mrs. Thornton, who was wary of Margaret's southern haughty ways, is galled by Margaret's rejection of her son.
Margaret's long-absent brother, Frederick, wanted for naval mutiny, secretly visits their mother as she is dying. Thornton sees Margaret and Frederick together and assumes he is her lover. Later, Leonards, a man from Helstone, recognises Frederick at the train station. An argument ensues and Frederick pushes Leonards away. Leonards dies shortly after. The police question Margaret about the scuffle: she lies and says she was not there. As the magistrate investigating Leonards's death, Thornton knows Margaret lied but declares the case closed to save Margaret from the humiliation of possible perjury. Margaret knows his deed on her behalf and is greatly humbled. She no longer looks down upon Thornton but begins to recognise the depth of his noble character.
Nicholas, on Margaret's prodding, approaches Thornton for a job which he eventually gets. Thornton and Higgins learn to appreciate and understand each other better. Mr. Hale visits his oldest friend Mr. Bell in Oxford. There, Mr. Hale also dies and Margaret must go back to live in London with Aunt Shaw. She visits Helstone with Mr. Bell and requests him to tell Thornton about Frederick. But Mr. Bell dies before he can do so and leaves Margaret a considerable legacy that includes Marlborough Mills and the Thornton house.
Thornton is forced to stop production as a result of market fluctuations and the strike. He learns the truth about Margaret's brother from Nicholas Higgins and comes to London to settle his business affairs with Margaret. While Margaret presents Thornton with her business proposal, Thornton recognises that Margaret is no longer indifferent to him. They realise that they are both in love and decide to marry.