Lawrence Selden, a bachelor lawyer, views the exquisitely beautiful Lily Bart, a socialite who is expected to inherit vast sums of money from her wealthy aunt, and who is further anticipated to marry a man of vast wealth. Lily is twenty-nine years old and worries that her physical beauty is fading, which means that her chances for marrying an eligible wealthy man are also becoming slimmer. An orphan, Lily lives with her wealthy aunt, Mrs. Peniston, a miserly woman who refuses to give her niece an allowance.
Selden and Lily retire to Selden's apartment for tea and discuss the relative drawbacks to womanhood. Lily reveals to Selden that her manner has served to put off a potential mother-in-law, who has since sent Lily's prospective fiancé to India. Both Selden and Lily agree that the social functions they attend are boring affairs. Upon leaving Selden's apartment, Lily meets Simon Rosedale, a bachelor whose wealth continues to grow staggeringly, but whose presumptuous demeanor Lily finds repulsive.
Lily attends a weekend party at the country home of Judy and Gus Trenor, where she attempts to cement an engagement to the wealthy — and boring — young bachelor Percy Gryce. Lily turns her attentions to Selden, but finds that she has competition from Bertha Dorset, a married guest who has designs on Selden. Lily and Selden have a conversation in which it is decided that he is not wealthy enough to marry Lily. In the meantime, a bitter Bertha sabotages Lily's chances with Gryce by shocking him with the knowledge that Lily plays cards for money. On a ride to town, Trenor tells Lily that he will invest money for her with no financial risk.
Lily is approached by a cleaning woman who has recently been fired from the building where Selden lives. Believing that Lily is the woman responsible for writing love letters to Selden, the woman wishes to sell the letters to her. Lily purchases the letters and discovers that they have been written by Bertha. In the meantime, Trenor's investments on Lily's behalf are paying off, and Rosedale continues trying to court Lily. Grace Stepney, Lily's cousin, is embittered by Lily's removal of Grace from a dinner party attendance list, and proceeds to tell Mrs. Peniston that Lily has been gambling and spending extravagantly. She also tells Mrs. Peniston that there are rumors that Lily is receiving money from Trenor, in effect making her a "kept woman."
