Tracy Lord is the elder daughter of a wealthy Philadelphia Main Line socialite family. She was married to C.K. Dexter Haven, a yacht designer and member of her social set, but divorced him two years prior because, according to her father, he does not meet the standards that she sets for all her friends and family. She is soon to marry the wealthy George Kittredge.
In New York, Spy magazine publisher Sidney Kidd is eager to cover the wedding and assigns reporter Mike Connor and photographer Liz Imbrie. Kidd intends to use the assistance of Dexter, who has been working for Spy in South America. Dexter tells Kidd that he will introduce them as friends of Tracy's brother Junius, a diplomat in Argentina. Tracy is not fooled, but Dexter tells her that Kidd has threatened the reputation of her family with an innuendo-laden article about her father's affair with a dancer. Tracy deeply resents her father's infidelity, which has prompted her parents to live separately. Nonetheless, to protect her family's reputation, she agrees to let Mike and Liz stay and cover her wedding.
Dexter is welcomed by Tracy's mother Margaret and teenage sister Dinah, much to Tracy's frustration. She soon discovers that Mike has admirable qualities and finds his book of short stories in the library. As the wedding nears, she finds herself torn among George, Dexter, and Mike.
The night before the wedding, Tracy becomes drunk, kisses Mike and takes an innocent midnight swim with him. When George observes Mike carrying Tracy into the house afterward, he assumes the worst. The next day, George tells her that he was shocked and feels entitled to an explanation before proceeding with the wedding. She admits to having no excuse and realizes that he does not really know her and has loved her as an idealized, perfect angel, so she cancels the engagement.
Tracy realizes that the guests have arrived and are waiting for the wedding ceremony to begin. Mike quickly volunteers to marry her, but she graciously declines because she perceives that Liz is in love with him. Dexter then offers to remarry her, and she gladly accepts.
