Lights, camera, action!
Rain Man starts out being more about a self-centered guy named Charlie Babbitt than the dude referenced in the title—in fact, when we start out, we have zero idea who the "Rain Man" even is. It's all about this money-obsessed yuppie who's trying to make a killing selling Lamborghinis… and isn't very good at it, apparently, since his cars are tied up in a conflict with the EPA and unable to get to their buyers.
Then, Charlie's dad dies, and he and his girlfriend/business associate, Susanna, go back to Cincinnati to settle his dad's estate. Charlie is shocked—and more than a little angry—to learn that his dad left him basically squat. All he got was a car and some rosebushes, and the rest of Father Babbitt's estate was put into a trust for some unnamed person. Charlie had never gotten along with his dad, and this posthumous slap in the face doesn't make him feel any warmer or fuzzier toward the guy.
Charlie starts hunting for this anonymous beneficiary of the trust, and the quest leads him to a hospital called Wallbrook. There, he discovers that his father's money was left to a brother he never knew he had. His name is Raymond, and he'd been entrusted to the hospital's care for years because he was autistic.
Unsurprisingly, Charlie isn't super excited about having a brother, and he doesn't seem terribly patient with Ray's particular challenges. But he decides to use the situation to his advantage and basically kidnap Ray away from the hospital. The goal? Hold him ransom to get the half of the inheritance that he thinks should have gone to him out of Doctor Bruner, who served as the trustee of Ray's money.
We're sure this'll end well.
Ray isn't a big fan of planes, so he and Charlie end up going on an extended road trip back to L.A. Charlie's girlfriend is so disgusted with Charlie's treatment of Ray that she bows out early on and leaves the two of them to their own devices. Charlie has a lot of trouble warming up to Ray at first, especially since he really doesn't understand or have any patience with his brother's special needs, but eventually they end up bonding (particularly when they go to Vegas, and Raymond's gifts come in handy at counting cards).
Through all this, Charlie's desire to have his brother around as a bargaining chip morphs into a desire to have his brother around because he actually cares about him.
Surprise mushiness, guys.
Charlie becomes less of a jerk, and he manages to find some semblance of a family through Ray. So instead of trying to steal Ray's money, he decides to fight for custody of Ray, even though Doctor Bruner (Ray's physician/trustee back at Wallbrook) thinks it's a terrible idea.
The courts end up agreeing with Doctor Bruner that Ray has too many challenges to live outside of a hospital setting, and Raymond returns to Wallbrook. The bright side? Charlie's total reformation from a greedy, kidnapping toolbox to a loving brother.
Turns out you don't need a woman to reform a rake.