The Custom of the Country (Modern Classics)

The Spraggs, a family of midwesterners from the fictional city of Apex who have made money through somewhat shady financial dealings, arrive in New York City at the prompting of their beautiful, ambitious, but socially-naive daughter, Undine. She marries Ralph Marvell, a member of an old New York family that no longer enjoys significant wealth. Before her wedding, Undine encounters an acquaintance from Apex named Elmer Moffatt, a character with "a genuine disdain for religious piety and social cant". Undine begs him not to do anything that will endanger her wedding to Ralph. Elmer agrees.
Although Ralph dotes on Undine, his finances do not permit the extravagant lifestyle Undine desires, and she feels that her in-laws scorn her. When she becomes pregnant, she is disconsolate; and she neglects her son, Paul, after he is born. Alone in Europe, Undine begins an affair with the nouveau riche Peter Van Degen, who is married to Ralph's cousin, Clare.