John immediately regrets his treatment of Esther and looks for her night after night to no avail. He is worried that Mary has become too much like her aunt and decides that it is time for his daughter to marry. However, Jem Wilson is set to marry Molly Gibson, and John scolds Mary for missing her chance with him. Mary, meanwhile, is still focused on Harry Carson. Later that evening, Jem, dressed in his finest suit, comes to propose to Mary. He tenderly offers his heart and hand in marriage, but Mary remains silent. She tells him that she can never be his wife. Heartbroken, Jem tells Mary not to blame him if he becomes a drunkard or a murderer. Later, Mary falls to the floor, violently sobbing, realizing that she loves Jem more than her life. At midnight, she retreats to her room and makes plans to tell Jem how she really feels.
At work the next day, Mary avoids Sally Leadbitter and ignores Harry's advances. Sally pays an unexpected visit to Mary’s home and conveys the message that Harry will not take no for an answer. Mary goes with Sally to meet Harry and tells him face-to-face that she does not want to see him anymore. Harry, though, refuses to let her go - offering to marry her if that is what it takes to continue their relationship. Upon finding out that Harry never intended to marry her in the first place, Mary is that much more strong in her rejection. When Mary leaves, Harry informs Sally that he will not give Mary up without a fight, but he will not propose to her again.
Jem, meanwhile, is miserable and contemplates enlisting in the army, but he cannot abandon his mother and Aunt Alice, who rely on him. Harry continues to send Mary letters though Sally, but Mary keeps sending them back unopened. Mary waits for Jem to come back to her, but he never shows up. Meanwhile, she must work all night to earn enough to support herself and her father - whose opium addiction is deepening. Margaret, who has been away on a concert circuit, stops to see Mary. Margaret shares the news that she has seen Jem in Halifax - he has invented a crank, which his master bought and patented. Margaret discourages Mary from writing to Jem about her feelings for him - instructing her to be patient. Margaret kindly gives Mary some money, which she uses to buy much needed provisions. The next day, Mary follows Margaret’s advice to visit Jane Wilson. Alice is now nearly blind as well as deaf. Jane brings up Jem’s invention, but Mary quickly changes the subject. Soon, Will arrives at the house to everyone’s joy. They have tea and before Mary departs, Alice tells her to wait patiently on the Lord.
A few days later, Will Wilson fetches Mary because his aunt wants him to meet Job Legh and Margaret. She learns that Jem has been in a state of depression since his return from Halifax. To her disappointment, Jem is not at the gathering. The evening turns out to be a merry one, because Will and Job have a lively argument about the existence of mermaids. Will claims that a shipmate of his from the John Cropper once saw a mermaid. Later, when Margaret sings, Will is entranced by the beauty of her voice. The evening ends with Will telling the group that he will soon set sail for America. Mary returns home, thinking of her depressed father, Harry, her ex-lover who continues to assail her, and her beloved Jem, whom she has not seen since his return.
At the end of Esther’s imprisonment, she seeks out someone she can warn about the danger Mary is headed towards. She finds Jem Wilson and tells him of Harry Carson’s intentions for Mary. Jem thanks Esther and offers to bring her home so she can escape from her life of prostitution. However, Esther confesses that she is addicted to alcohol and urges Jem to try to save Mary instead. Esther mournfully tells Jem her story - she ran off with a soldier, had his child, and then he deserted them when his regiment moved. Her young daughter grew ill and Esther had to give up the wares shop she had set up. When the young girl died, Esther turned to street-walking to make a living. Jem later regrets not having insisted that Esther come to his home and get off the streets.
John Barton's days drag on - he is hungry, hopeless, and desperate. His abject hatred of the upper class continues to grow, and his bitterness starts to bring out the monster within. Soon, a foreign market puts in a request for goods from Manchester, which brings work into the mills at last, although the same client puts in a duplicate order in a nearby manufacturing town where the mills charge much less. Therefore, the mill owners in Manchester are forced pay their workers extremely low wages in order to remain competitive, but they do not explain these measures to the workers. The underpaid, disgruntled workers organize a strike. As a result, the mill owners are forced to hire weavers from the surrounding countryside who are then terrorized by the striking Manchester men.
Harry Carson joins the faction of mill owners who oppose all concession to the strikers, all the while insisting to Mary that he will have her. John Barton joins a deputation of men who will negotiate with the mill owners for higher wages. As Mary pines away for Jem, she notices that Will Wilson is in love with Margaret. One day, Jem approaches Harry and asks him about his intentions towards Mary. Harry finds out that Mary rejected Jem and taunts him with this information. Harry says it his intentions for Mary are no business of Jem’s and calls Mary an arrant flirt. Jem refuses to leave until Harry shares his intentions so Harry strikes him with his cane. Jem throws Harry to the ground, and a policeman arrives, breaking up the fight. Jem walks away - still threatening Harry.
Jem’s proposal spurs Mary Barton to return to a virtuous path, swaying her away from making the same mistakes that her Aunt Esther has made. Mary shows that she has matured when she is finally able to separate infatuation from real love, abandoning her dreams of being Harry Carson's wealthy wife and realizing her unconditional love for Jem Wilson. Unfortunately, Mary makes her decision too late and feels as though she has lost Jem for good. The agony of their separation is Mary's penance for her flirtatious past. She is pained by Jem’s accusation that if his life ends badly, it will be her fault. By burdening Mary with his future sins, Jem plays Adam to Mary's Eve - connecting back to the Biblical idea that women are to blame for the sins of men.
Will Wilson provides an international perspective in Mary Barton, which until this section has focused strictly on life in Manchester. Will is an uncommon representation of a sailor, because most Victorian writers portrayed men of the sea as nefarious rascals who have different lovers in every port. Margaret Jennings, with her sweet nature and angelic voice, is Will’s mermaid, the complete opposite of the common trope that all sailors are after a sexually depraved siren. Margaret represents the ideals of feminine virtue because she possesses inexhaustible goodness. By positioning Margaret as a confidante and guide for Mary, Gaskell implies that Mary should strive to be more like Margaret and not Esther.
Meanwhile, Alice's gathering gives Gaskell an opportunity to show that for Victorian intellectuals, science was quickly replacing folklore. According to the educated and practical Job Legh, mermaids do not exist. Through the character of Job, Gaskell dispels the stereotype that everyone in the lower class is ignorant and uninformed.
In this section, Gaskell compares John Barton to Frankenstein’s monster. This is because Gaskell does not indict the lower classes for making immoral decisions. Rather, she believes that the cruel, uncaring world has made John Barton into a monster, when he had once had so much raw potential for caring and goodness. Gaskell's “purpose piece” for the novel is that all the class strife stems from the fact that the upper classes did not care to understand why their less fortunate counterparts wanted to strike or lash out. Gaskell saw this disconnect as the root of all the class conflict in her country. Through her novels, she intended to shine a light on the struggle of lower-class families and humanize them in order to bring unity to a polarized society.
Jem's interrogation of Harry brings out the differences between the two. Jem may be poor and brutish at times, but he loves Mary and has always wanted to be with her. Despite his meager station in life, Jem is a noble, moral man who works hard to support his family. In comparison, Harry Carson is spoiled and used to getting what he wants. He is selfish and superficial. In this characterization, Gaskell reveals her bias towards the blue-collar characters in her novel. She has set up Jem as a diamond in the rough, and Mary's ascension from adolescent girl to mature woman is in her realization that Jem's good heart is worth a great deal more than Harry's lavish lifestyle.