Undine Spraggs is a precious, capable young woman. She convinces her family to move from a small town in the midwest all the way to bustling New York City. Immediately she bids her family goodbye in order to marry a socialite from a formerly wealthy family, Ralph Marvell. She desires all the benefits of having married rich, but she soon discovers that Marvell is just not financially equipped to provide for her taste in that way. She soon grows tired of married life, detesting her in-laws, resenting her husband, and feeling sorry for herself. She gives birth to a son, Paul, but barely pays him any attention.
Undine takes a trip to Europe, leaving Paul and Ralph behind. She starts an affair with Peter Van Degen, a wealthy man over there. He's actually a mutual acquaintance of Ralph's since he's married to Ralph's cousin, Clare. Needless to say their relationship is going nowhere fast, but Undine tries to trap him into marrying her by immediately divorcing Ralph and telling him everything. Peter, however, is unable to divorce Clare, and dismisses Undine. She's now a widow with no prospects, so she moves back to the States and the midwest specifically.
She's a resourceful gal, however, and soon makes her way in society once more. Soon she's in Paris where she meets Raymond de Chelles and seduces him. Like all her previous affairs, Undine desires the money more than the man. He has fallen for her charms, but he cannot marry her because she's divorced and he's Catholic. Undine decides to try and bribe the Pope, using money blackmailed from Ralph in threat of taking custody of their son if he doesn't pay, to annul her previous marriage. Ralph has to borrow money from a man named Elmer Moffat in order to pay Undine. Distraught over his increasing debts and the threat of losing Paul, Ralph kills himself. Now Undine can marry Raymond because she's technically a widow, so she promptly does.
As things turn out, Undine used to be married to Moffat. When they both lived in the midwest, long before New York, they had eloped together and quickly gotten divorced. Undine's predatory pattern is predictable. Moffat had visited her right before her marriage to Ralph, but he had decided to stay out of her affairs. Oddly enough he is the one to fund her bribe for the Pope, and he's the one left holding the bag after Ralph dies without paying his debts.
Undine quickly realizes that Raymond, too, is not wealthy enough to suit her needs. His family is old money, meaning most of their assets aren't liquid. She doesn't have the extravagant spending money she wants, so she must stay in the French countryside much of her time instead of in Paris on shopping sprees. Once more, she divorces. . . only to re-marry Moffatt this time. At least they know each other well enough to have real expectations for the marriage. Moffatt is many times richer than he was during their first marriage, but still Undine ends up dreaming of how much happier she would be as an ambassador's wife.