Rain Man is the story of two brothers who meet after the death of their father. The younger brother, Charlie, is a money-minded machine who is angry that he didn't get all of his father's inheritance for himself. His older brother, Raymond, is an autistic savant who is brilliant but cannot live on his own. In order to get Raymond's portion of the inheritance, Charlie decides to kidnap Raymond from the institution where he has been living for many years.

Charlie and Raymond travel across the United States from Cincinnati to Los Angeles in their father's old Buick Roadmaster. As the two get to know one another, they finally become true brothers. For Charlie, this moment comes when he realizes that he remembers Raymond as the "Rain Man" of his childhood. Charlie's transformation begins from that moment, and he cares less about money and more about his brother...