The narrator reveals Mr. Harthouse's inner thoughts about this step in his relationship with Louisa; he isn't deliberately planning a wicked seduction, but he's bored by everything in his life except this fascinating, attractive woman, and means to continue to try to gain her confidence.
Harthouse isn't so much evil as he is careless and selfish. He's not out to ruin her, but he's not concerned if he does. For her part, because of the industrial, fact-based world Louisa has grown up in, she is vulnerable (especially as a woman) to a show of human, sympathetic feelings from any party…in this case, from Mr. Harthouse.
Riding home after a day of work, Harthouse encounters an upset Bounderby, who reveals that the Bank has been robbed! Only 150 pounds have been stolen, which is very little compared to Bounderby's wealth, but naturally Bounderby is as enraged as if it had been all of his holdings. As they talk, the two men meet Louisa, Mrs. Sparsit, and Bitzer on the path. Harthouse and Louisa both instantly suspect Tom, though neither voices it. Mr. Bounderby, Mrs. Sparsit, and Bitzer suspect Stephen Blackpool, who was observed lurking around the Bank multiple times at night for no apparent reason.
Mr. Bounderby's ridiculous greed is betrayed by his disproportionate outrage at being robbed of so small a sum of money. Furthermore, it becomes clear to the reader that a poor factory worker, Stephen, has been taken advantage of to shield the real perpetrators of the crime from justice…another abuse of the factory workers by the system.
Mrs. Sparsit claims that her nerves have been shocked by this event, and moves temporarily back in with Louisa and Mr. Bounderby. She also takes to calling Louisa "Miss Gradgrind" instead of "Mrs. Bounderby". That night, while Mrs. Sparsit comforts Bounderby at home, Louisa and Mr. Harthouse go for a walk outside.
Mrs. Sparsit seems to be trying to reassert herself in Bounderby's life, and by calling Louisa "Miss Gradgrind" she is stating that Louisa isn't really married to Bounderby. Note that when Louisa feels upset she goes walking with Harthouse, who has shown far more sympathy to her than Bounderby ever has.
Then, long after everyone has gone to bed, Tom finally returns. He finds his sister awake and waiting for him, but upon pleas for him to confide in her, he sulkily and resentfully maintains that he's not hiding anything. He hints that Louisa should mention neither the visit they paid Stephen, Rachael, and the old woman, nor the conversation that Tom had with Stephen that night. Louisa sorrowfully leaves after Tom refuses to say anything more, and upon her departure, Tom cries tears of guilt and self-pity…but he is not penitent.
Because Tom had no moral upbringing (only a fact-based one), he practically has no conscience. Though he seems to be aware when he does wrong, he is indifferent to it insofar as he is not harmed. He cares only about himself.