The House of Mirth is the story of Lily Bart, a woman caught between two dominating passions. The first is to live in wealth as part of the 1890s-era New York aristocracy, while the second is to find a man with whom to have a respectful and loving relationship. Lily is unable to reconcile her desires and slowly destroys her standing in society, becoming addicted to sleeping draughts and eventually dying alone of an overdose.
Lily Bart, a beautiful but impoverished socialite, is on her way to a house party at Bellomont, the country home of her best friend, Judy Trenor. Her pressing task is to find a husband with the requisite wealth and status to maintain her place in New York society. Judy has arranged for her to meet the wealthy though boring Percy Gryce, a potential suitor. Lily grew up surrounded by elegance and luxury—an atmosphere she cannot live without as she has learned to abhor "dinginess." The loss of her father's wealth and the death of her parents left her an orphan without inheritance or a caring protector. She adapts to life as ward of her straight-laced aunt Julia Peniston from whom she receives anerratic allowance, a fashionable address, and good food, but little succor.
Additional challenges to her success in the“marriage market” are her advancing age—she has been on the "marriage market" for ten years, her penchant for gambling at bridge leaving her with debts beyond her means to pay, her efforts to keep up with her wealthy friends, her inner most desire to marry for love as well as money and status,and her longing to be free of the claustrophobic constrictions and routines of upper crust society.
Lily’s week at Bellomont ends up in a series of failures beginning with losing a large sum at bridge. She also loses her ploy to marry Percy Gryce even though her relationship with him during the week goes so well, everyone thinks an engagement between them is imminent. There are threats to her reputation because of her risky decision to visit her friend Lawrence Selden’s Manhattan flat during the two-hour wait for the train to Bellomont. On departing, she unfortunately encounters Mr. Rosedale, a Jewish businessman known to her set. Attempting to cover the appearance of an indiscretion, she professes to have been consulting her dress-maker. On her last day at Bellomont, threats to Lilly’s social standing begin when she agrees to have Gus Trenor make investments for her with the small amount of money she has. Lacking financial knowledge Lily truly believes Gus is making investments onher behalf and accepts several large checks from him. On several occasions, however, Gus makes it clear that he expects romantic attention from Lily in exchange for his financial expertise. She begins playing cat and mouse with him resulting in her public appearances at opera and late afternoon walks in Central Park with him. In retribution for a social snub, Lily’s cousin Grace Stepney informs their aunt Julia about rumors that Lily has gambling debts which she may be trying to cover through an inappropriate relationship with Gus Trenor. This sows seeds of doubt and discomfort in Aunt Juliawho though shocked, does not discuss the situation with her niece so as to avoid a scene.
Lily's failure with Percy Gryce occurs when at week's end the tall, handsome and engaging Lawrence Selden unexpectedly shows up at Bellomont. Lily chooses to spend Sunday afternoon with him instead of meeting Percy for morning church services and an afternoon walk. Even though she made it clear to Selden during their tête-à-tête in his flat that she looked at him as that friend who won’t be afraid to say disagreeable things to her, she becomes drawn to him romantically. Succumbing to her agreeable femininity, Selden begins to fall in love with Lily, yet realizes that she cannot marry a man of his modest means.
Her strategy to marry Percy Gryce is thwarted by Bertha Dorset who is still wildly interested in Selden with whom she has been carrying on an extramarital affair. When she realizes that Selden came to Bellomont to see Lily, Bertha retaliates by making sure Percy finds out about Lily's gambling, smoking, and borrowing money from men to pay off her gambling debts. Percy gets scared off and soon thereafter marries Evie Van Osburgh. Mrs. Dorset's public pride in her match-making victory makes Lily subject to social ridicule. Lily decides not to burn Bertha's love letters to Selden, which she purchased from the char woman at Selden's apartment house who mistook Lily for Selden's paramour.
Lily attempts to neutralize the deleterious effects of the gossip surrounding her by renewing her association with her nemesis, Bertha Dorset, attending an unsuccessful house party at Bellomont, and cooperating with Carrie Fisher’s mission to bring the newcomers, the Wellington Brys, into high society. Following Mrs. Fisher’s advice, the Wellington Brys throw a large "general entertainment" featuring a series of tableaux vivants portrayed by a dozen fashionable women in their set including Miss Bart. The pièce de résistance of this highly successful event turned out to be the portrayal of Mrs. Lloyd in Sir Joshua Reynolds' famous 18th-century painting (1775–1776). The portrait shows an attractive woman suggestively clad. As the curtain opens on this last scene the gasp of approval heard from the audience was not as much for Reynold's brilliant interpretation of Mrs. Lloyd as it was for the loveliness of Lily Bart herself —marking the pinnacle ofher social success. As Selden observes her in this tableau —elegant in its simplicity— it is as if for the first time he sees the real Lily Bart and feels the desire to be with her. He finds her alone in the ballroom toward the end of the musical interlude as the collective praise from her admirers was subsiding. He leads her to a garden where he tellsher he loves her and they kiss. Lily sighs, " 'Ah, love me,love me—but don't tell me so!' " (141) and takes her leave. As Selden gathers his coat to leave he is disturbed by Ned Van Alstyne's remarks, ". . . .Gad, what a show of good-looking women; but not one of 'em could touch that little cousin of mine. . . . I never knew till tonight what an outline Lily has.” (142)
The next day Lily receives two notes—one from Judy Trenor inviting her to dine that evening at her town house and the other from Selden asking to meet with her the following day. Though she had a dinner engagement, she agreed to a visit with Judy at ten o'clock. However, her late-evening encounter turns out to be with Gus alone. Gusvehemently demands the kind of attention he thought he had paid for. Pleading naivité about business matters and appealing to their friendship, she promises to pay back the almost $10,000 she owes him. With heightened anger and resentment, he accuses Lily of playing with him while entertaining other men. Lily gets him to back off and gets herself into a hansom cab. Shaken and feeling very much alone, she calls on her friend Gerty Farish for succor and shelter for the rest of the evening. The following day Lily pleads with her aunt to help her with her debts and confesses that she has lost money gambling at bridge even on Sundays. her Aunt Julia refuses to help her except to cover the $1,000 to $2,000 bill for clothes and accessories. Feeling trapped and disgraced, she turns to thoughts of Selden and his love as her savior and has a change of heart towards him as she looks forward to his visit at four o'clock.
Instead, her visitor turns out to be Simon Rosedale who, so smitten by her appearance in the tableau vivant, proposes a marriage that would be mutually beneficial. Considering what Rosedale knows about her, she skillfully pleads for time to consider his offer Selden does not appear for his 4:00 appointment nor does he send word in explanation. Instead he has departed for Havana and then on to Europe on business.
To escape the rumors arising from the gossip caused by her financial dealings with Gus Trenor, and also disappointed by what she interprets as Selden's emotional withdrawal, Lily accepts Bertha Dorset's spur-of-the- moment invitation to join her and George on a Mediterranean cruise aboard their yacht, the Sabrina. Bertha intends for Lily to keep George distracted while Bertha carries on an affair with young Ned Silverton. Lily's decision to join the Dorsets on this cruise proves to be her social undoing.
In order to divert the attention and suspicion of their social circle away from her, Bertha insinuates that Lily is carrying on a romantic and sexual liaison with George by commanding that she not return to the yacht in front of their friends at the close of a dinner the Bry's held for the Duchess in Monte Carlo. Selden helps her arrange for lodging for the night with her cousin Jack Stepney under the promise that she leave promptly in the morning, The ensuing social scandal ruins Lily's reputation and almost immediately causes her friends to abandon her and Aunt Julia to disinherit her. Undeterred by such misfortunes, Lily fights to regain her place in high society by befriending Mr and Mrs Gormer and becoming their social secretary, so as to introduce the Gormers to high society and groom them to take a better social position. However, her enemy, the malicious Bertha Dorset, gradually communicates to them the "scandalous" personal background of Lily Bart, and, so, undermines the friendship which Lily had hoped would socially rehabilitate her. Only two friends remain for Lily: Gerty Farish (a cousin of Lawrence Selden) and Carry Fisher, who help her cope with the social ignominy of a degraded social status, whilst continually advising Lily to marry as soon as reasonably possible.
Despite the efforts and advice of Gerty and Carry to help her overcome notoriety, Lily descends through the social strata of the high society of New York City. She obtains a job as personal secretary of Mrs. Hatch, who is a disreputable woman and who very nearly succeeds in marrying a wealthy young man in Lily's former social circle. She resigns after Lawrence Selden returns to warn her of the danger, but not in time to avoid being blamed for the crisis. Lily then finds a job in a milliner's shop; yet, unaccustomed to the rigors of working class manual labour, her rate of production is low and the quality of her workmanship is poor, and she is fired at the end of the New York social season when the demand for fashionable hats has ceased.
Meanwhile, Simon Rosedale, a Jewish suitor who earlier had proposed marriage to Lily, when she was higher in the social scale, returns to her life and tries to rescue her, but Lily is unwilling to meet his terms. Simon wants Lily to use love letters, which she bought from her servant, to confirm the occurrence of the love affair between Lawrence Selden and Bertha Dorset. For the sake of Selden's reputation, Lily does not act upon Rosedale's request, and secretly burns the love letters when she visits Selden, one last time.
Eventually, Lily Bart receives a ten-thousand-dollar inheritance, from her Aunt Peniston, with which she repays Gus Trenor. Distraught by her misfortunes, Lily had begun regularly using a sleeping draught of chloral hydrate to escape the pain of poverty and social ostracism. One day, Lily takes an overdose of the sleeping draught and kills herself. Hours later, Lawrence Selden arrives to her quarters, to finally propose marriage, but finds Lily Bart dead; only then is he able to be close to her.