The Spraggs, a family of newly wealthy midwesterners from Apex, arrive in New York City to advantageously marry off their beautiful, ambitious, and temperamental daughter Undine.

Attracted to glamour and extravagance Undine has a hard time making inroads into the high status old money social circles she wishes to enter.

Convinced that Undine is a simple and plain spoken girl who would be ruined by her elevation in society, he resolves to quickly woo and marry her.

Four years later, Undine misses her son Paul's birthday, causing Ralph to realize that he is no longer in love with her.

Unable to cover her bills, Undine accepts a loan from Peter Van Degen, the nouveau riche husband of Ralph's cousin Clare.

She later learns from a friend that, while Clare never would have agreed to a divorce, the reason that Peter dropped Undine was that he discovered Ralph was deeply ill and was pleading for her to come home.

His cousin Clare points out that, rather than legally fight for custody, he should offer Undine a large amount of money to keep Paul.

The de Chelles are hidebound aristocrats, their wealth tied in land and art and antiques that they will not consider selling, and Undine cannot adjust to the staid customs of upper-class French society.

She also resents having to spend most of her time in the country because her husband cannot pay for expensive stays, entertainment, and shopping trips in Paris.

Charles Bowen asserts to Laura Fairford that it is "abnormal" that Ralph Marvell does not share his business life with his wife Undine.

Upon receiving the Edith Wharton Lifetime Achievement Award in 2012 in Boston, Massachusetts, Fellowes said: "It is quite true that I felt this was my book; that the novel was talking to me in a most extreme and immediate way.

In Undine Spragg, Wharton has created an anti-heroine absolutely in the same rank as Becky Sharp, Scarlett O'Hara, or Lizzie Eustace.

One scholar writes: "Her rise through the ranks of New York society from the nouveau riche demonstrates her ability to use marriage and divorce in order to achieve her desire for social dominance."

"Wharton personifies consumer culture through Undine Spragg, demonstrating how individual agency gets lost when involved in the system.

[citation needed] Ralph Marvell recognizes the poetry in the name and assumes it refers to the poetic French phrase "divers et ondoyant" meaning "diverse and undulating".