Soon after Judge James K. Hardy sentences some Carvel High School boys to write a 20,000 word essay as punishment for distributing anti-authority leaflets, he is approached to go to Washington to work on an important case. J. J. Harper of the federal government offers to pay Judge Hardy two hundred dollars a day plus expenses to hear a case involving utility company monopolies. Though Emily Hardy is suspicious of such a high salary, she and the family accompany her husband to Washington where they are given the "V.I.P." treatment. Andy is smitten with young Suzanne Cortot, the daughter of the French ambassador, while Marian is intrigued by the sophisticated lifestyle of John Lee and his wife Margaret. The Lees, who are lobbyists for the utility companies, befriend Marian, hoping to hear inside information on the case. Because Emily is worried that Marian's head may be turned by the glamour of Washington, she convinces the judge to send for her boyfriend, Wayne Trent, an engineer who can help the judge with the complicated case. When Wayne arrives, Marian thinks that he is merely following her, and they have a serious quarrel. Meanwhile, Andy visits museums and learns French in his pursuit of Suzanne. When she invites him to her cotillion, he realizes that he needs a tuxedo but doesn't have the twenty-five dollars needed to buy one. After he borrows enough from his father and Wayne to pay for it, however, Judge Hardy learns that Andy had also been distributing the leaflets at school. The judge then takes Andy to see Mount Vernon, George Washington's home, and makes his son realize the triviality of his leaflets in comparison with the work of the founding fathers. As a punishment for not admitting his guilt, the judge "sentences" Andy to thirty days without his tuxedo, with the exception of the cotillion. Andy goes to the cotillion and teaches the staid society teenagers the "Big Apple," and they discover that they like Jazz better than waltz music. Meanwhile, Marian foolishly speaks about the case to the Lees and they record her conversation, then take her words out of context. The next day, Lee goes to Judge Hardy with the record to blackmail him, but the judge throws him out. When an item about Marian's remarks gets into a gossip column, stock in the utility companies rise, and the judge decides that they must return to Carvel. Back home, he also realizes that because Marian's comments will make it seem as if he were going to profit from the rise in stock prices, he must resign from the bench. Before he resigns, however, Andy talks to him and makes him realize that he must fight for what is right. Judge Hardy then arranges to make a radio broadcast and announces that the commission has decided against the utilities company. He also says that he had "planted" Marian to learn more about their illegal monopoly. Finally, with the Hardy family safely home, Marion reconciled with Wayne and Andy back to his hometown girl friend, Polly Benedict, life returns to normal in Carvel.