At the Bellomont, Lily and Mrs. Trenor are gossiping as usual. Mrs. Trenor tells Lily that Percy Gryce has left Bellomont because he felt snubbed when Lily canceled her walk with him to spend time with Selden. Worse, Gryce's departure may have been influenced by Bertha Dorset, who told Gryce about the "skeletons" in Lily's closet as well as her serious financial problems related to gambling debt. Lily thought she could simply spend one day with Selden and the rest of her stay with Gryce in at attempt to win him over, but her hopes of marrying him are not yet defeated. Still, she knows that Gryce has become a topic of conversation among the women at the Bellomont, most of whom find him disagreeable. Lily also realizes that she is accruing enormous debt from gambling and buying nice clothes, so she decides to return to the house of her aunt, Mrs. Peniston, as soon as possible.

Before leaving, Lily goes to the train station to pick up Gus Trenor, coming home to the Bellomont from a business trip. As they talk on the ride, the topic of Wall Street and investment comes up. Knowing that some of her friends have had success with stock market speculation, Lily decides to ask Trenor to invest some money for her. Trenor assents, although we later find out that he is interested in helping Lily because he is sexually attracted to her. Lily confesses to him that she is considering marriage to Gryce, about which Trenor expresses disgust. She admits that she needs more financial security and is no longer able to stay at the Bellomont.

The Wall Street speculation works initially; Lily begins receiving checks, which she uses to pay off her various gambling and clothing debts. She feels a sense of superiority over women such as Carry Fisher, who rely on the rich men with whom they flirt to pay off their debts. Several weeks after she begins investing, Lily's cousin Jack Stepney marries Gwen Van Osburgh. At the wedding, Lily meets Gerty Farish, a socially inept and generally disliked cousin of Selden who spends a lot time with him. Lily learns to her horror that Gryce and Evie Van Osburgh, the youngest Van Osburgh daughter, have been courting one another since they met at the Dorsets' house under the invitation of Bertha Dorset. Lily now knows that Bertha actively tried to prevent her marriage to Gryce.

Financially, Lily's investments continue to produce money; Lily receives another check for $4,000. Trenor invites her to return to the Bellomont to stay for several weeks, but Lily refuses his offer at first. He also encourages her to be friendly to Simon Rosedale, to whom Lily is ordinarily rude because she dislikes him intensely, as we see in a meeting between the two.

Chapter Nine introduces us to Mrs. Peniston and her house at Richfield, which Mrs. Peniston cleans thoroughly once every autumn. At her aunt's house, Lily has ample time to wander and think about her social situation, and she decides to stay away from the Bellomont until the Christmas holidays because the people there have become bored with her, knowing her too well.

Later that fall, Lily receives a visit from Mrs. Haffen, the woman who worked as a maid at the Benedick, where Selden lives. She presents to Lily a collection of letters written to Selden which he had not properly destroyed after reading. The letters, written by Bertha Dorset, are presumably love notes she wrote to Selden when they were having an affair (though this is never said explicitly). Realizing the letters could hurt Selden if they fell into the wrong hands, Lily purchases them from Mrs. Haffen and decides to destroy them. Before she can do so, however, Mrs. Peniston returns from Stepney's wedding and announces that Bertha was personally responsible for arranging the marriage between Evie Van Osburgh and Gryce. Realizing that the letters could also be used to blackmail Bertha, Lily decides to save them in her drawer so that they can be used to her advantage later.

Lily's conversation with Mrs. Trenor in Chapter Seven provides a good example of how the past plays an important role in present society. We learn that Carry has been associated in the past with two European nobility figures, Prince Varigliano and Lord Hubert. We learn later that Lily was once engaged to the prince, but the engagement was broken at the last minute when Lily was caught flirting with another man. Lily has a number of skeletons in her closet, all of which Mrs. Dorset knows about and will use to harm Lily when the occasion arises. The past is never forgotten in this society; it can always come back to haunt anyone.

Lily also begins to get a sense that she is sliding back toward her old life, before she was an aspiring member of society. This foreshadows her upcoming social decline; at the end of the novel she has been removed from society altogether and joins the working classes. However, we should also note how frequently Lily's mood changes in the novel. She is usually at one extreme or another: freedom or slavery. Interestingly, both states are based on her financial status. When Lily has come into money, she feels wholly free. Whenever she feels burdened by debt, she feels enslaved. Earlier on in the novel, when Lily is staying at the Bellomont, she even asks herself whether the maid who helps tidy the Bellomont is better off than she, because the maid is not a slave to debt, clothing and gambling like Lily. The freedom-versus-slavery motif comes up frequently in later chapters, particularly when Lily faces the problem of how to pay off her debt to Gus Trenor.

As discussed in the Context section, The House of Mirth was written just over a decade before the emergence of the Modernist movement, which took an interest in the workings of the mind, among other things. Modernism saw the development of the stream-of-consciousness style used by Virginia Woolf, T.S. Eliot and William Faulkner. Some of the roots of that interest in the workings of the mind also can be seen in Wharton, who includes a map of Lily's thought process in Chapter Seven. When Lily hears about the stock market, she immediately thinks about whether or not it could benefit her. To decide this, she thinks about her friends and whether or not they have benefited, which also answers the question of whether or not the stock market would be a socially acceptable concept. Deciding that her friends have profited from stocks, Lily decides that she too should get involved. She then has to figure out who will help her, and she realizes that Trenor can take care of her finances without compromising her social standing at all because Trenor is already married. She then asks Trenor to help her, and he readily assents. Thus, every step of Lily's thought process involves a calculation of how an idea could benefit her and whether or not her friends have also made use of the idea. This is an important insight into Lily's value system as a character and an effective literary technique on the part of Wharton.

One of Wharton's tasks in the novel is to portray some of the ironies of society, most of which are related to money. Ideally, because Lily needs money the most in order to join society, she should be the one who marries a rich man such as Gryce. Instead, Gryce marries Evie Van Osburgh, a woman who is already extraordinarily wealthy and has no need for money. It is also ironic that even though Lily and Selden love one another, Lily feels that she cannot marry him because he does not have enough money. In the latter case, society's emphasis on social stature and money places people in situations that force them to act against their will.