As socialite Tracy Lord is meticulously preparing for her impending wedding to the uptight George Kittredge at her picturesque Newport, Rhode Island estate, her ex-husband, the charming millionaire songwriter C. K. Dexter-Haven, sets the stage for a jazz festival right next door, using his own home as a vibrant rehearsal hall. Just the night before her big day, Tracy confides in her inquisitive younger sister, Caroline, revealing that she has decided not to invite their father, Seth Lord, as he has chosen to abandon their mother for a much younger chorus girl.
Tensions rise when Tracy hears Dexter playing a nostalgic tune that they cherished during their time together. Fueled by a mix of nostalgia and frustration, she storms into his home and confronts him, accusing him of orchestrating the festival solely to disrupt her wedding festivities. With an air of vulnerability, Dexter confesses that he still carries deep feelings for her, gently reminding her of the reason their marriage crumbled—her high expectations that he could never fulfill. In a heated exchange, Tracy disparages him, stating that instead of becoming a respected composer, he has sold out to become merely a "jukebox hero," and storms away in frustration.
Meanwhile, back at the Lord residence, Uncle Willie relays a disturbing message to Tracy’s mother, Mrs. Lord, revealing that Spy magazine plans to suppress a scandalous article about Seth's infidelity, which could tarnish their family's name, on the condition that they are allowed to cover Tracy's elite wedding. In a desperate bid to safeguard her family’s reputation, Tracy agrees to this morally questionable arrangement. Shortly after, the reporters Mike Connor and Liz Imbrie arrive, only to be met with exaggeratedly awkward niceties from Tracy and Caroline as they skirt questions regarding their father.
As the evening unfolds, both George and Dexter appear at the Lord residence, prompting Liz to seize the moment for a photograph of Tracy positioned between her former and future husbands. Reluctantly, Tracy complies, but in a moment of rebellion, she knocks over the camera, ruining the photo opportunity entirely. In her mounting frustration, Tracy introduces her Uncle Willie as "papa" to deflect the press’s questions about her real father. The family plays along with this charade, and when Seth finally arrives, they refer to him as Uncle Willie, further complicating the already fraught family dynamics.
Amidst the opulent chaos, Mike and Liz confide in one another, sharing their mutual discontent with the trappings of wealth, stating that they would prefer genuine happiness over the hollow affluence that surrounds the Lords. As one challenge leads to another, Dexter urges Tracy to lower her standards for George, acknowledging her intolerance for "human frailty." In a private moment, Tracy unwraps a wedding gift from Dexter—a miniature model of their dream yacht—causing a wave of bittersweet memories to crash over her of their early, whirlwind romance.
Just as Tracy grapples with her emotions, George interrupts her contemplative moment, vowing his unwavering devotion to her, which makes her realize the extent of his idealization. Feeling misunderstood, Tracy demands to be seen as a real woman and confronts Seth about his past behavior. In a shocking twist of events, Seth deflects responsibility, suggesting that his unfaithfulness is a misguided attempt to cling to youth and insinuates that Tracy has contributed to this distance by withholding her affection.
Feeling lost and overwhelmed by the complexities of her day, Tracy, in a haze of alcohol, invites Mike for a drive, hoping to convince him that his views on the upper-class society of Newport are misguided. When they detour to Uncle Willie’s house for a drink, Tracy confesses how sheltered her wealth has made her. In what seems like a pivotal moment, Mike passionately suggests that all she needs is the right man to stir her heart. However, when Mike leans in to embrace her, the reality of her situation dawns on Tracy, prompting her to withdraw.
After returning home, the enchantment of a serenade from Dexter stirs her emotions anew, reminding her of the affection she still harbors for him. Later that evening, at the lively bachelor party hosted at Uncle Willie’s, the jazz rhythms of Louis Armstrong and his band fill the air, contrasting sharply with the tensions between George and Dexter. When George discovers that Tracy has gone missing, a frantic search ensues, leading him to an unexpected scene where a tipsy Mike, carrying a soggy Tracy, returns from the pool, igniting a confrontation fueled by jealousy and misunderstanding.
The next morning, the frantic preparations for the wedding begin, but Tracy awakens with no memory of the previous night's escapades. In a quiet moment, she seeks counsel from Dexter, who wisely shares that mistakes can often illuminate relationships. Just then, Mike and Liz announce their newfound resolve to abandon their sleazy journalistic endeavors, while George's wavering confidence about marrying Tracy hangs in the air.
Upon questioning Tracy about last evening’s mysterious incidents, Mike clarifies to George that it was merely a case of two innocent kisses and a spontaneous swim, further leaving Tracy feeling cornered and defensive about her perceived image. When George, basking in self-righteousness, extends his forgiveness, Tracy realizes that marrying him is the true mistake, boldly stating that she "couldn't bear a perfect man."
As the wedding music begins to play, Tracy is prompted to articulate a speech to her guests. With a mix of nervous energy and spontaneity, she inadvertently reveals that she eloped with Dexter years prior and announces her intention to marry him instead in a grand ceremony. Ecstatic at the unexpected turn of events, Tracy embraces Dexter, gratified by their rekindled love, while Mike and Liz, inspired by this leap into love, decide to tie the knot, as a jubilant rendition of the wedding march fills the air, celebrating the triumph of love over societal expectations.
