Young love rocks a staid Boston family.

In 1912, Boston Brahmin George Apley inhabits a world circumscribed by the exclusive boundaries of Beacon Hill. George, who considers himself an arbiter of propriety, exhibits more concern for the trivialities of bird watching or his wife Catherine's "radical" Thanksgiving table arrangement of snap dragons and pumpkins than political or social issues. To uphold the Apley proud tradition of insularity, George has sent his son John to Harvard and is in the midst of engineering a proper marriage between John and his cousin, Agnes Willing. As the family gathers for Thanksgiving dinner, George is displeased that his headstrong daughter Eleanor has chosen to dine with her suitor, Howard Boulder. When George's acerbic sister Amelia arrives with her droll husband Roger, Amelia is scandalized that Howard is from New York rather than Boston. Soon after, the dowdy Agnes arrives, accompanied by her mother Jane and snobbish father Horatio. At dinner, George voices his horror upon discovering that Henry Apley, a distant family member, has had the temerity to bury his mother Hattie in the family plot and has insisted that the grave be moved. After dinner, John abruptly excuses himself, and after he leaves the house, George finds a perfumed note that John dropped. George is disturbed that the note is from a woman who lives in Worcester, a foreigner by George's standards. As he bids his guests goodnight, George is flabbergasted to see Eleanor and Howard cavorting in the snow. Afterward, Eleanor informs her father that she is in love with Howard and cites the work of Sigmund Freud as the rational for her emotional display. Horatio, meanwhile, investigates John's Worcester paramour, Myrtle Dole, and reports that her family has had the bad taste to place an iron deer on their front lawn. Upon discovering that Howard, a lecturer at Harvard, is giving a course on his idol, Ralph Waldo Emerson, George attends one of Howard's talks. Incensed by Howard's radical interpretation, George arranges to have him fired. Furious, Eleanor informs her father that she plans to marry Howard and he responds that the marriage is entirely unsuitable. Later, at Agnes' coming out party at the Apley house, John tells Agnes that he is in love with someone else. Distraught, the love-sick Agnes runs off in tears. Catherine consoles the girl by recalling her similar experience years earlier, when her then fiancé George fell in love with an Irish girl from South Boston. After George's father sent him abroad, George came to his senses and Catherine assures her that John will, too. Roger, meanwhile pulls George aside and informs him that he has been denied the presidency of the bird watcher's club because of his callous behavior in the cemetery incident and in the firing of Howard. Criticizing George's narrow view of the world, Roger reminds him of his long lost love and counsels him to be more understanding of his children. Taking Roger's advice, George writes a letter of apology to Henry, permits Eleanor to date Howard and encourages John's courtship of Myrtle. After informing Horatio that John plans to marry Myrtle, George arranges to meet Myrtle's father Julian at the Apleys' exclusive men's club. There, Julian, a self-made iron magnate, comments on George's complacency. When George proposes that the Doles rent an apartment in Boston to prepare the Apleys' social circle for John's impending engagement, Dole declares that the marriage would never work and announces his intention to ship Myrtle off to California and thus end the courtship. Dole's statement jars George back into his myopic world, and he proclaims that Eleanor will be sent abroad and John will marry Agnes. Some time later, Eleanor returns from Europe to attend her brother's wedding and finds Agnes suffering from self doubt. After Eleanor advises Agnes to shed her stodgy clothes in favor of a more contemporary look, George takes his prospective daughter-in-law to New York on a shopping trip. There, with George's support, Agnes transforms her appearance. While strolling down the street one day, they meet Howard, who ridicules George for his provincialism. Afterward, Agnes sympathizes with the shaken George and praises his loving warm qualities. On the day of the wedding, George and Agnes return from New York with Howard in tow. After escorting Eleanor to the waiting Howard, George gives them his consent to marry and presents then with two steamer tickets that were reserved for John and Agnes' honeymoon. Upon entering the church, George greets Henry, who is seated in the family pew. As a radiant Agnes walks down the aisle, John beams at his soon-to-be bride.