In the mid-1800's, in New York's Washington Square, wealthy widowed physician Austin Sloper bemoans the fact that although his daughter Catherine has had superior schooling and training, she lacks the refined qualities of her beautiful mother, and is "an entirely mediocre creature."  Austin consequently asks his sister, widow Lavinia Penniman, to encourage his homely daughter to become more social.

That night at a party, Austin's other sister, Elizabeth Almond, and her husband Jefferson, announce the engagement of their daughter Marian to Arthur Townsend, an eligible bachelor.  Arthur's handsome and charming cousin Morris surprises Catherine by asking her to dance.  Although she is clumsy, Morris is deferential and full of flattery, and before the evening's end, he asks to see her again.  Morris becomes a frequent visitor at the Sloper home during the ensuing week, and Austin is reservedly pleased that someone is taking an interest in his spinster daughter.

One night, Lavinia ignores Austin's request that she chaperone them, and when she leaves Morris and Catherine alone together, he proposes.  Catherine accepts without hesitation, despite Morris' warning that her father may think he is a mercenary because he is unemployed, uneducated and frittered away his inheritance in Paris.  Instead of having her suitor request her father's permission as convention dictates, Catherine announces her engagement to Austin, who then sends for Morris' sister, Mrs. Montgomery.  Austin's suspicion that Morris is after Catherine's substantial inheritance is confirmed, despite Mrs. Montgomery's reticence to condemn her wastrel brother.  Austin is outraged that his naïve daughter is being duped and is deaf to Catherine's earnest pleas that she is in love, forbidding the marriage.  To distract her, he convinces Catherine to accompany him to Europe for six months, and Morris vows to wait for her.

While Austin and Catherine are away, Morris visits Lavinia at the Sloper home, and settles in to a luxurious life style.  After a few months, Austin realizes that Catherine still clings to her love, and they return to New York.  When Catherine insists on marrying Morris despite his threats to disinherit her, Austin angrily tells his daughter that because she is homely and dull, her only attraction is her money, and that her only talent is her neat embroidery work.  Shocked by her father's cruel disdain, Catherine plans to elope with Morris that night, and reveals to her fiancée her father's threat.  Although Catherine is ready and waiting at the appointed hour, Morris never shows up.  Lavinia, who acknowledges that Morris is a fortune-hunter, feels that he at least offered Catherine a small chance at happiness, and chides her niece for revealing her disinheritance.

A week later, Austin falls ill with heart disease, and Catherine learns that Morris has borrowed money to move to California.  The shock of rejection leaves Catherine heartless and cold, and she refuses to see her father even as he lays dying.  Despite Austin's prior threats, Catherine receives her full inheritance after his death.

Years later, Morris returns to see Catherine. Although she initially refuses him entry to the house, she changes her mind when she hears his voice.  Morris then begs her forgiveness and attempts to vindicate himself by saying that he left in order to keep her from losing her inheritance.  When Catherine reservedly grants her forgiveness, Morris boldly proposes again, saying that he needs her love, and Catherine encourages him to elope that night.  However, after he leaves, she tells Lavinia that she intends to reject Morris so that he will never return.  She then steadily works on the embroidery sampler she began when Morris first abandoned her, and finishes just as he knocks on the door at the hour of their rendezvous.  Ignoring his entreaties, Catherine douses the light, bolts the door from the inside, and climbs the stairs to her room, turning her back on Morris.