The novel opens in Grand Central Station, where the protagonist, Lily Bart, is waiting for a train to Bellomont, the home of Gus Trenor and his wife, Judy Trenor. As she waits, she is spotted by her friend Lawrence Selden. He invites her to have tea with him at his flat, the Benedick. Over tea they discuss a number of issues, including the roles of men and women in society and marriage, two of the larger issues with which the novel concerns itself. We learn that Selden is not particularly rich and that he has an interest in collecting Americana, or American books, although his limited financial resources prevent him from building as large a library as he would like.

Lily leaves Selden to catch her train to Bellomont, but as she leaves the building she encounters an acquaintance, Simon Rosedale, who we learn is a social climber. Rosedale asks why Lily was at the Benedick, and, not wanting him to suspect any courtship between herself and Selden, she lies to him, telling him that she was visiting a dressmaker in the building—which he knows to be false. Later, on the train, she realizes that she should have told him the truth that she was having tea with a friend, but because of her lie, Rosedale now suspects that Lily may be trying to cover up something.

On the train, Lily finds an acquaintance, Percy Gryce, an eligible young bachelor also on his way to the Bellomont. Lily sits next to him and begins a conversation. We learn that Gryce is also interested in book-collecting, although he is apparently more wealthy than Selden. He is described as a well-mannered young man. Their conversation is interrupted by the arrival of Bertha Dorset, an obnoxious gossip also on her way to Bellomont. She sits down with Lily and Gryce, although Lily obviously does not care for her company.

At the Bellomont, we are introduced to an array of characters, all of whom are in the upper-crust New York social elite. The main social activity is gambling money on games of bridge. Lily gambles for a while, but stops when she realizes that she has almost run out of money, calculating that she lost $300 just that evening. We learn that she is not very wealthy compared to some of the other guests, who can afford to lose large sums gambling. The issue of money makes Lily think back to childhood memories. Her mother raised her, teaching her to make the most from few financial resources. Her father was out of the picture for much of her youth; her only real memory of him is of the day he came home from work and announced to the family that he was financially ruined. Her mother tried to conceal their lack of money from Lily, and she blamed her husband for ruining the family even after he died. After Lily's mother died too, Lily's aunt, Mrs. Peniston, took care of Lily when no one else would, taking her to live in New Jersey and treating her very kindly. Nevertheless, Lily's childhood experiences with her mother left her with a hatred for "dinginess," or lack of wealth, which she may have to face if she continues to lose money gambling.

The first few chapters of the novel introduce some of the most important thematic elements that will recur throughout the novel. The House of Mirth is a novel of manners, or a novel that focuses on social conventions and the quest to get married (See "The Novel of Manners" section for more). The book deals with the world of an elite New York society that evaluates its members constantly to determine whether or not they are still worthy of membership. As a result, even the tiniest details of a person's actions are scrutinized by other members of the society. The opening paragraphs of chapter one provide a good example. Selden sees Lily standing alone in a train station, evaluates some possible reasons for her presence, then decides to test her, walking past her to see if she was attempting to hide. Indeed, Wharton tells the reader that Lily's "simplest acts seemed the result of far-reaching intentions."

The theme of constant judgment also comes up at the end of the chapter, when Rosedale questions Lily's presence at the Benedick, and fearing that he may gossip about a possible affair between her and Selden, Lily quickly lies to cover up the truth. Immediately, we see that the social world is one of mean-spirited mind games and lies, in which people cannot be trusted.

Because details are so important to the characters in the novel, the reader should be prepared to read the novel very closely, keeping in mind that we as readers are meant to think about each detail just as the characters themselves do. This is why Wharton focuses on so many minutiae, most notably things such as Lily's two major facial motions: smiles and blushes. These two motifs come up regularly throughout the novel and take on different meanings, always providing good clues to Lily's feelings.

The first chapter also gives us a sense of the type of language, or diction, that is used throughout the novel. The narrative also uses a number of epigrammatic short, witty sayings that are meant to entertain the reader while providing social satire. For example, Lily jokes that Selden has rescued her from a dull afternoon, and he cleverly replies that it is his mission in life to do so. In Chapter Four, Mrs. Trenor remarks paradoxically that "it's much safer to be fond of dangerous people." (This is the same technique used by Oscar Wilde to convey social commentary in his plays.)

In a larger context, The House of Mirth was written after the publication of Charles Darwin's On the Origin of Species, a book which introduced to the world the concept of survival of the fittest, an idea that works well with The House of Mirth's depictions of social acceptance. Chapter One incorporates the language of Darwin's ideas of natural selection, when Lily begins to think "how highly specialized she was" and that ugly people must, in some mysterious way, have been "sacrificed to produce her."

Chapter Three introduces us to the novel's gambling motif, which will also become very important later in the novel. We are told that Lily has lost almost $300 in that night and is in dire financial straights as a result. Later on, Lily's obsession with gambling will lead her to become involved with the stock market, another form of gambling in which people are ruined financially. It is important to notice that when Lily starts to think of her lack of money, she immediately looks back to her childhood. We begin to see that Lily inherits many of her traits from her mother, who was concerned with keeping up the appearance of wealth even when none existed; when Lily's father announced that he is ruined, the very first words out of Mrs. Bart's mouth were an order for Lily to shut the door so that the servants would not begin to doubt their wealth. Mrs. Bart even tried to cover up their relative indigence to Lily, telling her that her father was merely tired and didn't know what he was saying.

Much like her mother, Lily is obsessed with maintaining the appearance that she is wealthy even when she may not be. Her absolute fears, then, are rejection from the society and "dinginess," which her mother also dreaded. Lily's goal is to end up in a socially prestigious and financially sound marriage. The novel is comprised of a series of circumstances that lead to her rejection from society and eventual death.