In a mansion called Xanadu, part of a vast palatial estate in Florida, the elderly Charles Foster Kane is on his deathbed. Holding a snow globe, he utters his last word, "Rosebud", and dies. A newsreel obituary tells the life story of Kane, an enormously wealthy newspaper publisher and industry magnate. Kane's death becomes sensational news around the world, and the newsreel's producer tasks reporter Jerry Thompson with discovering the meaning of "Rosebud".
Thompson sets out to interview Kane's friends and associates. He tries to approach his second wife, Susan Alexander Kane, now an alcoholic who runs her own nightclub, but she refuses to talk to him. Thompson goes to the private archive of the late banker Walter Parks Thatcher. Through Thatcher's written memoirs, Thompson learns about Kane's rise from a Colorado boarding house and the decline of his fortune.
In 1871, gold was discovered through a mining deed belonging to Kane's mother, Mary Kane. She hired Thatcher to establish a trust that would provide for Kane's education and assume guardianship of him. While the parents and Thatcher discussed arrangements inside the boarding house, the young Kane played happily with a sled in the snow outside. When Kane's parents introduced him to Thatcher, the boy struck Thatcher with his sled and attempted to run away.
By the time Kane gained control of his trust at the age of 25, the mine's productivity and Thatcher's prudent investing had made Kane one of the richest men in the world. Kane took control of the New York Inquirer newspaper and embarked on a career of yellow journalism, publishing scandalous articles that attacked Thatcher's (and his own) business interests. Kane gives financial management although not operational control of his newspaper empire to Thatcher after the 1929 stock market crash left him out of cash.
Thompson interviews Kane's personal business manager, Mr. Bernstein. Bernstein recalls that Kane hired the best journalists available to build the Inquirer's circulation. Kane rose to power by successfully manipulating public opinion regarding the Spanish–American War and marrying Emily Norton, the niece of the President of the United States.
Thompson interviews Kane's estranged best friend, Jedediah Leland, in a retirement home. Leland says that Kane's marriage to Emily disintegrated over the years, and he began an affair with amateur singer Susan Alexander while running for Governor of New York. Both his wife and his political opponent discovered the affair, and the public scandal ended his political career. Kane married Susan and forced her into a humiliating operatic career for which she had neither the talent nor the ambition, even building a large opera house for her. After Leland began to write a negative review of Susan's disastrous opera debut, Kane fired him but finished the negative review and printed it. Susan protested that she never wanted the opera career anyway, but Kane forced her to continue the season.
Susan consents to an interview with Thompson and describes the aftermath of her opera career. She attempted suicide, and so Kane finally allowed her to abandon singing. After many unhappy years and after being hit by Kane, she finally decided to leave him. Kane's butler Raymond recounts that, after Susan left him, he began violently destroying the contents of her bedroom. When he happened upon a snow globe, he grew calm and said "Rosebud". Thompson concludes that he cannot solve the mystery and that the meaning of Kane's last word will remain unknown.
Back at Xanadu, Kane's belongings are cataloged or discarded by the staff. They find the sled on which eight-year-old Kane was playing on the day that he was taken from his home in Colorado and throw it into a furnace with other items. Behind their backs, the sled slowly burns and its trade name, printed on top, becomes visible through the flames: "Rosebud".
