A political boss faces changing times as he runs for re-election.

Frank Skeffington, the Irish-American mayor of a large New England city, descends his staircase, pausing, as he does every morning, to place a fresh rose by the portrait of his deceased wife. At the bottom of the stairs wait his secretary, the city wardheelers and various aides, and outside the office door is the usual crowd of noisy constituents. Skeffington's staff notes that Amos Force's newspaper opposes the mayor's recently announced bid for a fifth term, even though the two major opposing candidates are unimpressive: Charles J. Hennessey, a longtime but harmless opponent, and Kevin McCluskey, a young naval hero with few ideas of his own. In Force's newsroom, the sour old publisher is planning a series of articles in support of McCluskey, not because he respects the younger candidate but because he despises Skeffington. Adam Caulfield, the writer of the paper's popular sports column and Skeffington's nephew, asks his uncle why Force so dislikes him. Skeffington reveals that his own mother, once a maid in the home of Force's father, was humiliated and then fired by the elder Force for stealing two overripe bananas and a small apple, a "crime" usually accepted by the wealthy Yankees who employed poor Irish immigrants. The Force family had never forgiven their maid's son for becoming mayor of the city. During this conversation, Skeffington asks Adam to cover his re-election campaign "from the inside." Uninterested in politics, but fascinated by his sometimes unethical but always humane uncle, Adam agrees, much to the chagrin of his wife Maeve and her father, Roger Sugrue. Nevertheless, Adam's respect and affection for his uncle, emotions not expressed by Skeffington's playboy son "Junior," increase as he attends rallies and other campaign events. At the wake of Knocko Minihan, Adam is at first outraged when Skeffington fills the widow's house with his supporters, who hand out cigars while conducting ward business. Skeffington's manager, John Gorman, explains that while admittedly trying to promote his campaign, Skeffington has nonetheless succeeded in packing the wake of the universally disliked Minihan with well-wishers, a fact that deeply touches the grieving widow. When Adam later hears Skeffington threaten to take greedy undertaker Johnny Degnan before his licensing board unless he reduces the high cost of the services, Adam becomes his uncle's avid supporter. After the funeral, Skeffington learns that the city's bankers have decided not to provide the loan needed to clean up one of the city's worst slums. Furious, he and his cronies invade the exclusive Plymouth Club, where banker Norman Cass, Sr. is lunching with a group of Skeffington detractors, among them Force and Bishop Gardner. Skeffington begs the men not to use the housing project as a political football, but Cass and his associates remain adamant. That afternoon, Skeffington flatters Cass's simpering son into becoming the fire commissioner. The next day, the mayor shows the elder Cass a photograph of his son, looking particularly foolish in his fireman's helmet, and asks, "Do I announce the appointment?" Cass agrees to provide the loan in exchange for the embarrassing photograph. Soon the Plymouth Club becomes the site of McCluskey's campaign headquarters, and the young candidate begins to make numerous television appearances. On the night before the election, Skeffington has dinner with Adam and Maeve and finally succeeds in charming the young woman. After the couple votes, however, she smilingly refuses to reveal her choice to her husband. As the returns begin to come in, Skeffington's campaign headquarters is noisy and upbeat, but it soon becomes apparent that McCluskey has won the election by a landslide. After hearing the television reporter describe the election as the biggest political upset in the city's history, Skeffington warmly congratulates his opponent and announces that he now plans to run for governor. The mayor then walks home alone as McCluskey's raucous victory parade fills the streets. Shrugging sheepishly at the portrait of his wife, Skeffington begins to climb the stairs but suddenly suffers a heart attack and collapses. The next day, as Skeffington rests in bed, scores of well-wishers appear outside the mayor's residence. Though his doctor orders him to see no one, Skeffington insists on saying goodbye to his old friends. Sugrue disdainfully asserts that if he had it to do over again, Skeffington would surely live his life differently. Barely able to open his eyes, Skeffington exclaims, "Like hell I would!" and dies.