Plot
Seventeen-year-old Daphne Reynolds is an American girl, living with her wedding singer mother, Libby, above a restaurant in Chinatown, Manhattan. Many years earlier, Libby had met Briton Henry Dashwood in Morocco, and they had gotten married in a Bedouin wedding ceremony, under uncertain legality. They then returned to his family's estate in England. His father died soon afterward, making Henry the new Lord Dashwood, Earl of Wycombe. Alistair Payne, the family's aristocratic advisor, tricks Libby into leaving Henry, telling her it is best for Henry's duties not to know she is pregnant; then he lies to Henry, hiding the pregnancy from him, and saying that Libby's claim for leaving him was because she had fallen in love with someone else.
Libby has always been honest with Daphne about who her father was, though Daphne felt a sense of emptiness without him. Daphne soon graduates from high school and she runs off to London to try and meet her father. Henry has disclaimed his seat in the House of Lords to run for election to the House of Commons, hoping to eventually become the Prime Minister of the United Kingdom. Henry is being pushed by Alistair, acting as his political advisor. As a result, Henry has become engaged to Alistair's snobbish daughter, Glynnis, who only wants to marry Henry in order to become the new Countess of Wycombe, who also had an equally snobbish and bratty teenage daughter, Clarissa.
Checking into a London hostel, Daphne meets Ian Wallace, a local boy who works there to support his dream of becoming a musician. After forming a friendship when Ian shows Daphne around London, they start dating. When Henry catches Daphne at his estate, he is stunned to learn he has a daughter, but his mother, Jocelyne, the current Countess of Wycombe, immediately welcomes her in, giving her a room at the estate. After confirming things in a phone call with Libby, Henry embraces the opportunity to connect with her. Daphne tries to win the acceptance of her father's social circle, but is repeatedly thwarted by Glynnis and Clarissa, who feel threatened by her arrival. In addition, Daphne has to ward off the advances of a boy, Armistead Stewart, a sleazy and arrogant upper-class boy whom Clarissa fancies and with whom Ian has long-standing rivalry. Daphne eventually pushes Armistead into the River Thames.
Daphne inadvertently wins over the British aristocracy, including an elderly royal, Princess Charlotte, whenever she interacts with them. However, Henry's political campaign suffers due to Daphne's flamboyant behavior, and his subsequent misbehavior with her. He asks her to assume the more dignified manner of the Dashwood lineage, after which Henry's polling numbers quickly begin to improve. But Ian is disappointed in her new behavior, made worse when she attends the Queen's garden party instead of hanging out with him.
During her Debutante party, hosted by her father, who flies Libby over to attend, Daphne overhears Alistair telling Glynnis how he "got rid" of her mother. When Daphne confronts him, Glynnis locks her in another room. Glynnis then asks Ian, the band's lead singer, to announce the father–daughter dance, knowing Henry will have to dance with Clarissa. Libby frees Daphne, but when they see Henry dancing with Clarissa, Daphne rejects her new self, telling Henry she is returning to the United States. Sometime later, Henry surprises everyone by announcing that he is withdrawing from the election. As he leaves the press conference, Henry discovers that Alistair knew about Libby's pregnancy and manipulated their separation and punches Alistair in the face for concealing Daphne from him for seventeen years. Henry then breaks off his engagement to Glynnis and calls off the wedding.
Daphne is serving as a caterer at a wedding, where Libby is the singer. When the father–daughter dance begins, Henry shows up, telling Daphne that he loves her for who she is. Daphne embraces him, calling him "Dad" for the first time. Daphne finally gets the father–daughter dance she has been longing for her whole life. Henry informs Daphne that he has brought a large apology present for her—at which point Ian appears and asks her to dance. As Ian and Daphne dance, Henry apologizes to Libby, and the two also start dancing.
In the epilogue, Glynnis has married a wealthy nobleman, who bores her to death, Clarissa has married Armistead, who still womanizes, and Alistair now works on a London tour bus. Now able to be together, Henry and Libby are legally married in another Bedouin ceremony, while Daphne is accepted into the University of Oxford, still being in a happy relationship with Ian. The film ends with Daphne, Henry, Libby, Jocelyn, and Ian having a family picnic in the backyard.
