On V-E Day in 1945, celebrations are in full swing, showcased by archival footage featuring a speech from Winston Churchill. Within the walls of Buckingham Palace, Princess Margaret and Princess Elizabeth are yearning to partake in the festivities, tired of being confined to the "mausoleum" of royal duties. Although their mother, Queen Elizabeth, dismisses their plea, the girls' longing for freedom becomes evident. King George, initially hesitant, ultimately recognizes the need for his daughters to experience the pulse of the people and permits them to join the celebrations, albeit under military supervision.
The excitement bubbles over for Margaret, while Elizabeth approaches the outing with a mix of apprehension and enthusiasm. Navigating through thick crowds proves challenging for their limousine, but they finally arrive at an indoor celebration where they are formally introduced. There, amidst the upper crust of society, the princesses engage in stilted conversations—far from what they had hoped for, though Elizabeth maintains her poise and attempts to engage.
As the guards guarding the princesses become distracted by enticing women, Margaret seizes the opportunity to escape. Noticing her absence, Elizabeth follows suit, leading to an unexpected encounter on a double-decker bus. There, sitting next to Jack—an Air Force pilot who has served in Germany—Elizabeth introduces herself as "Lizzie," cautiously revealing minimal information. Tension arises as she attempts to locate her sister, interpreting Margaret’s attempts at sign language to determine their destination: Trafalgar Square.
Without a proper fare, Elizabeth gets on the bus free of charge, and Jack, embodying a gallant spirit, covers her cost. When they find themselves on the street, Jack helps her navigate through the bustling city. An unexpected incident occurs when Elizabeth breaks her heel, prompting Jack to lend his skills to fix it. Their first stop—a lively pub—becomes the scene of a heated exchange where Jack openly criticizes King George, leading to his ejection. Though Elizabeth cautions him against his harsh remarks, Jack shares his own burdens, grappling with the reality of loss and disillusionment with the war.
Meanwhile, Margaret has her own misadventures, meeting Raymond, a military man whose intentions are questionable. After a series of unfortunate events involving a drink that makes her dizzy, Margaret finds herself seeking refuge in an office where she confesses her identity and receives help.
As Elizabeth continues to search for her sister, she ventures into a deserted part of town, inadvertently putting herself in danger until Jack arrives just in time to protect her. The soldiers, meanwhile, have discovered the chaos of the missing princesses and scramble into action, stricken with panic as they prepare to face consequences at their commanding officer's hands.
Elizabeth and Jack eventually return to the palace, only to find a crowd gathered for King George's speech. Distraught over Margaret's continued absence, Elizabeth seeks out her sister, leading them through the vibrant Chelsea streets aboard a tugboat, outsmarting the night traffic.
As fate would have it, Elizabeth locates Margaret at a dance, reveling in the swing band’s tunes. However, Jack faces looming consequences after being pursued for his earlier decision to desert. Elizabeth, revealing her identity to the gathered soldiers, swiftly alters the situation and earns their respect, paving the way for all to escape trouble.
In a poignant exchange, Jack shares his story, indicating an urgent need to return to his mother, but there's still time for one more connection. The soldiers escort a tipsy Margaret home, where she faces parental disapproval, while Elizabeth and Jack share a genuine moment with his mother.
As the day breaks, Elizabeth returns to the palace with Jack, much to the dismay of King George and Queen Elizabeth. Nevertheless, Elizabeth charms her way into their approval, inviting Jack to join them for breakfast. During their meal, King George learns about the princesses’ adventures and reflects on the opinions of those outside royal circles, leading to a heartwarming conclusion where they express gratitude for Jack's care of Elizabeth.
With time running short, Jack prepares to return to base, but Elizabeth, showcasing her rebellious side developed over years of practice, takes the wheel and speeds him back just in time, an exhilarating end to an unforgettable night.
