Undine, the main character in Edith Wharton's novel The Custom of the Country, craves money and social standing. She is undereducated, vacuous, and selfish. She uses her beauty to tempt men into improving her life and repeatedly hurts people when they stand in the way of her goals.

A creation of the social customs of her time—during which women were seen merely as mothers, homemakers, and ornaments—Undine knows that the only way to increase her wealth and social status is to marry the right man. On the surface, she is the perfect ornament. Underneath, Undine is crude, selfish, ambitious, and cruel. The men who love her eventually find out that they were initially blinded by her beauty and air of innocence.

Undine marries Ralph Marvell because his family has elite social status, and she focuses on this status instead of closely examining her future husband and his family (who do not share his infatuation with Undine). Ultimately, she gets bored by Ralph’s quiet, conservative life and looks for more excitement—and she has an extramarital affair with Peter van Daan, whose ostentatious wealth appeals to Undine. They plan to divorce their spouses and marry. Unfortunately for Undine, Peter van Daan notices her cold behavior toward Ralph during a serious illness and backs out of their plans.

Undine meets Raymond de Chelle in France, and he immediately falls in love with her. Undine hopes for marriage, not an extramarital affair, but Raymond and his family are Catholic and consider a divorced woman unmarriageable. Ralph commits suicide, which leaves Undine a respectable widow. She marries Raymond and briefly enjoys an exciting social life in Paris. She is indignant, however, when she has to leave her exciting Paris life and live in the country with his family. She resents her husband and ignores the financial realities of supporting a large family. Undine assumes he is being stingy and doesn't realize how much Raymond has come to loathe her.

Finally, Undine returns to the United States with a lover from her youth named Elmer Moffat. He is now a very rich man, and they quickly marry. The novel concludes with Undine’s encroaching boredom and disgust with Elmer Moffat. She now wants a cultured husband with a prominent role in society—and it is clear that she will never be fully satisfied.