Charlie Babbitt, portrayed by Tom Cruise, is a twenty-something car dealer from Los Angeles who finds himself in a bind while trying to import four gray market Lamborghinis. With the EPA threatening the deal, Charlie faces potential financial ruin. Just as he plans a weekend getaway to Palm Springs with his girlfriend, Susanna, played by Valeria Golino, he receives heartbreaking news: his estranged father, Sanford Babbitt, has passed away.
Traveling to Cincinnati, Ohio, to settle the family affairs, Charlie discovers an unexpected twist in the will—an undisclosed trustee is set to inherit a whopping $3 million on behalf of a beneficiary he knows nothing about. Instead, all he receives is a vintage Buick Roadmaster convertible and several prize-winning rose bushes. As tensions rise, he uncovers that the money is allocated to a mental institution housing his autistic brother, Raymond, played by Dustin Hoffman, someone Charlie never knew existed. This revelation strikes Charlie profoundly as he laments, > "Why didn't somebody tell me I had a brother?"
Despite his autism, Raymond exhibits remarkable memory skills, especially in mathematics, though he often lacks comprehension of the topics at hand. Some professionals refer to him as a savant. His world revolves around rigid routines and a deep discomfort with change, which is illustrated through his repeated recitation of the classic “Who’s on First?” comedy sketch. Emotionally reserved and avoiding eye contact, Raymond reveals layers of complexity that leave Charlie in a whirlwind of confusion and frustration.
Fueled by the desire to claim what he believes to be his rightful share of their father’s estate, Charlie embarks on a cross-country road trip with Raymond, circumventing air travel due to Raymond's phobia of flying. Charlie's original intention is to initiate a custody battle that would allow him to negotiate with Raymond's doctor, Dr. Gerald R. Bruner, in hopes of securing part of the inheritance for himself. This plan creates a rift with Susanna, who is disillusioned by Charlie's self-serving motives and ultimately decides to part ways in Cincinnati.
As the journey unfolds, Charlie learns more about Raymond’s condition, struggling to accept its authenticity and frequently growing frustrated with his brother’s quirks. Throughout their travels, stories from their childhood come to light, including song snippets of “I Saw Her Standing There” by The Beatles, which awaken memories of Raymond as Charlie's childhood guardian, misidentified as an imaginary friend named "Rain Man," a phonetic slip of "Raymond."
Charlie’s initial exploitative behavior becomes a point of transformation as he realizes Raymond’s immense value beyond financial gain. His foray into gambling in Las Vegas, exploiting Raymond’s counting abilities to win at blackjack, offers a glimpse into Charlie's changing character. By the end of their adventure, he begins to deeply care for Raymond, revealing a protective and loving side previously overshadowed by his greed.
Ultimately, when faced with his attorney to discuss inheritance claims, Charlie undergoes a profound shift, realizing that he truly desires to have his brother with him rather than any monetary reward. During a pivotal meeting with a court-appointed psychiatrist, cautioning Raymond about his decisions causes distress, leading Charlie to assertively protect his brother's well-being. In a bittersweet conclusion, Raymond returns to Cincinnati, and Charlie, having grown in his understanding, promises to visit him in two weeks, solidifying a newfound bond that transcends their earlier struggles.
