John Carson's mill is well-insured, so the fire makes little difference to his livelihood. In fact, the fire provides a perfect excuse for him to purchase new machinery and enjoy some leisure time with his family. However, Carson's workers, including George Wilson, are unemployed and driven deeper into poverty. While George is out of work, he must rely on Jem’s earnings at the forge. Both Wilson and John Barton are feeling the effects of the slack trade and scarce employment.
One evening near Christmas, George bursts into Barton’s home and asks his friend to help him bring food and medicine to Ben Davenport, one of Carson's former employees who has fallen gravely ill with typhoid fever. Barton takes his scant dinner and accompanies Wilson to the Davenports' dark, fetid cellar-home. Davenport is almost a corpse, tended to by his weeping wife and hungry children. Barton pawns all of his valuable possessions to buy food, candles and coal and brings the supplies back to the Davenports' cellar. Meanwhile, Wilson brings two of the Davenport children home with him, as Barton attempts to persuade the starving Mrs. Davenport to eat. Later, Barton goes to a druggist’s shop to purchase medicine. When he observes the affluence and cheer from outside the well-lit shop windows, John Barton becomes furious, but the narrator reminds the reader that no one can know the inner trials of other people simply from their outward appearances.
The next morning, Wilson goes to see Carson for an infirmary order. Wilson waits in the kitchen of Carson’s opulent home, taunted by the smells of rich food. He watches Mr. Carson and his handsome and son Harry enjoy their breakfast. Carson's youngest daughter, Amy, enters, embraces her father, and teases Harry for not buying her flowers she desires although he buys lilies for other girls, presumably Mary Barton. As Amy leaves, Wilson is announced and can finally enter the room. Carson gives Wilson an out-patient’s order and Harry gives his pocket change to the man. Carson's cook provides Wilson with a hot meal, and he returns to the cellar-home just in time to see Davenport die. Mary comes after receiving a message from her father and comforts Davenport's distraught widow. She prepares a mourning gown for Mrs. Davenport and Mrs. Simmons prepares for Davenport's funeral, which the town will pay for.
Just as Mrs. Davenport recovers from the shock of losing her husband and finds rent money through a local parish, the Wilson twins, who were never strong before, come down with typhoid fever. Margaret tells Mary about the twins' illness, and Mary feels guilty for being so involved in her flirtation with Harry Carson. Mary hurries to Ancoats, where the Wilsons live, and finds Jane Wilson with a dying twin on her knee and Alice crying over the dead body of the other child. George tells his wife to stop “wishing him” because no one can die in the arms of someone who wishes that person to live. Alice takes the boy from his mother so that he can die in peace. Alice comforts the family by telling them that the twins have been spared a hard life by the mercy of God. When Jem returns from work and hears the news, Mary is moved by his strong agony. Mary puts an arm on Jem’s shoulder and says she cannot bear to see him give way. Despite his pain, Jem feels the joy of her comfort and cannot refrain from taking her hand and telling her of his love. Mary, repulsed by his advances at such a time, returns to aid Alice and Jem ashamedly joins his parents, who are standing around their sons' twin corpses.
At dawn, Mary returns to her home, thinking about Jem. She wishes that his address had not been given so plainly or not given at all because she does not return his affection. Yet she cannot help but speak lovingly to him, although she usually tries to sound cross to avoid encouraging his attentions. Mary plans to help Jem when she is Mrs. Harry Carson. Shifting her thoughts to Harry, Mary drifts towards sleep and dreams about her future wealth as Harry's wife, and that she will be able to help her father. Mary sees Harry as her ticket to becoming a wealthy lady like her Aunt Esther. Three weeks later, Jem calls on the Bartons, dressed in his finest suit. Mary ignores his entrance and then retreats upstairs. Jem unwillingly starts a conversation about class struggles with John, who tells him that the majority of accidents occur in the last two hours of work, a sign that the working day should be shortened. Jem listens half-heartedly and departs with a vague excuse, his mind still on Mary’s withdrawn behavior.
John is left to muse on the sad state of trade and the indifference of the wealthy. Barton and his Chartist comrades believe that perhaps Parliament does not know of the conditions in Manchester. To remedy this presumed ignorance, the men form a petition in the spring of 1839 to gather witnesses to the deplorable destitution in manufacturing districts. John Barton is one of the appointed delegates and feels important and hopeful about the future. The night before the delegates’ departure to London, Barton holds a meeting for his neighbors, including Job Legh, to figure out what the delegates should say in Parliament.
The next morning, Mary sees her father off and considers her resolution not to see Harry Carson while John is away. This resolution rankles with both Harry and a Sally Leadbitter, who works with Mary at Miss Simmonds' place. Sally, a vulgar and forward girl, has acted as the go-between in Harry and Mary’s relationship. Sally walks to Mary’s house to deliver one of Harry’s letters and finds Mary in tears over the sudden death of George Wilson. Sally tells the distraught girl that Harry says he loves her, but Mary surprises Sally by saying that she does not think that she loves Harry at all. When Mary tells Sally about George's death, Sally makes a flippant comment about the brevity of life. Sally finally leaves after giving Mary the letter from Harry, imploring Mary to see him. Margaret Jennings arrives and the girls comfort each other over the death of their friend. Mary also finds out that the night before, Margaret earned a sovereign by singing for a man lecturing about music when his first singer became ill. Furthermore, Margaret is pleased because she finally told her grandfather about her growing blindness and he took the news well. Mary asks Margaret to sing and they dream about Margaret’s future career.
The next evening, John Barton returns home in a despondent mood because Parliament refused to listen to the delegation. Mary gives him the news of George Wilson's death, which deepens his gloom. Helplessly, Mary fetches Job and Margaret from upstairs to help cheer John up. Barton refuses to tell them about what happened at Parliament. Job tells the group his story about how he came to look after his orphaned granddaughter, Margaret. By the time Job finishes the story, Mary has fallen asleep on her father’s lap. She awakens and Job recites a poem from memory, which John asks Mary to copy down. The next day, Mary writes the poem on an old valentine that Jem once gave her.
The yoke of poverty grows steadily around the poor families of Manchester, including John Barton, who gave up his job in the factory for his fruitless journey to London. Now unable to find work, partly because of his involvement with the Trades’ Union, Barton struggles to pay the rent, forgoing food and pawning all of his possessions. Mary continues to work as a seamstress and often sees Harry, who still intends to make her his, one way or another. John's latent resentment soon grows to a rage and one day, he beats Mary for her insolence. He soon asks forgiveness and promises to never hit her again. Barton soon takes to chewing opium to numb his hunger pangs.
One evening, Barton tells Mary to visit Jane Wilson. Alice’s health has deteriorated and she is almost deaf. Jane Wilson scolds Mary for her negligence in not visiting her, a poor widow. Meanwhile, Alice shares the news that Jem has been made foreman because he improved a piece of machinery. Jane grows angry when Mary appears to snub Jem as a possible husband and attempts to tell Mary that she is not good enough for Jem. Mary changes the subject and tells Alice that she is grieved to find her so deaf and departs, wondering if Jem really cares for Molly Gibson, the girl that Jane claims Jem will marry. A few weeks later, a street-walker tries to speak to John when he is walking home after a union meeting. He tries to avoid her until he realizes that this woman is the long-lost Esther. He flies at her in a rage and flings her to the ground. A policeman comes and arrests Esther for what he believes to be drunkenness. Esther spends the next month in Bailey’s prison, worrying that her warning for the younger Mary will come too late.
The fire at Carson’s mill reveals the unequal distribution of hard times. When Carson loses his mill, he has the security of insurance money, and the time off ends up being a luxury, allowing him to be with his family. Gaskell's description of Carson's home is punctuated by the narrator's claims that it is not her place to judge. This statement alone reveals Gaskell's harsh judgment of the Carson's affluent lifestyle in the face of tragedy. However, the lower classes face a much more bitter trial when work is scarce. The Davenports’ cellar demonstrates the deplorable living conditions of the poor. Gaskell wrote these scenes based on her experiences as a minister’s wife and her observations of industrial town poverty.
The conditions of poverty in Mary Barton also serve to highlight the inappropriate and predatory nature of Harry Carson’s affection for Mary Barton, who is poor and uneducated. Her dreams of becoming a lady are hardly blameworthy, after considering the hardship she has endured her whole life. Harry’s pursuit of Mary illustrates a wanton disregard for her virtue, which in Victorian England would have dictated her worth as a bride. Gaskell does not remove all blame from Mary, who flirts knowingly with Harry, but shows that her actions are more due to ignorance than to immorality. Men and women were simply not considered intellectual equals, and Mary's characterization reveals this deep-seated bias.
John Barton’s trip to London is an important turning point for his character, because it is this trip that strips away his remaining faith in humanity. Barton, like Gaskell, believed that the upper class and Parliament did not do anything to alleviate the rampant poverty because they were ignorant to it. However, Barton's beliefs are shattered when it becomes clear that Parliament has no intention of hearing from England's poorest citizens and has instead simply let them suffer. While Barton may have failed in his efforts to enlighten Parliament, Gaskell did her best to give a voice to the poor by writing this novel. She desired to show the members of the upper class how terrible life was for those who did not earn a living wage. By telling the stories of the poor and downtrodden in Mary Barton, Gaskell uses her writing as a window into real life in these industrial downs. She shows the human side of poverty.
Meanwhile, addiction to illicit substances, like opium and alcohol, had started to become a prevalent problem in Victorian England, especially among the lower classes. There were few outlets for rehabilitation, and those who became trapped in the cycle of addiction had little means of escape. In this section, John Barton starts taking opium to reduce his hunger pangs, because the drug is cheaper than food. Similarly, Esther uses alcohol to numb her senses and thus tolerate her life as a prostitute.
John Barton’s meeting with Esther is an important turning point in Mary Barton. In this scene, Barton shows that he still blames Esther for Mary Sr's death, as well as revealing his growing tendency towards cruelty and violence. By this point in the novel, John Barton is firmly on a troubled path, and has certainly fallen from the grace and heroism he displayed in earlier chapters. He cannot fall back on the Christian principles of his youth and forgive his sister-in-law. However, Barton will pay dearly for his inability to pardon Esther, because she is only trying to help him protect Mary - but he cannot control his anger long enough to listen to her.