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 industrial 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 personal 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 to 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 him one of the richest men in the world. He 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 sold his newspaper empire to Thatcher after the 1929 stock market crash left him short of cash.