Harry's home alone, and Sally's at a big shindig, dancing rather lacklusterly with a boring but handsome man.
Harry takes a walk, and we hear his internal monologue. He's clearly trying to convince himself he's not miserable without Sally.
Sally's equally miserable at the party, and she wants to head home early.
Meanwhile, Harry eats sad ice cream and then throws the leftovers into a sad trashcan. Then he sadly puts his sad hands in his sad pockets.
He finds himself at the place that he and Sally parted ways when they first got to New York: Washington Square Park.
He flashes back on their entire relationship, and we hear their original conversation about how it's impossible for men and women to be friends.
Harry has a moment of clarity. He's realized something. Ah, we think we know what.
He takes off running.
Because this is a romantic comedy.
And that's what one does at the end of a romantic comedy.
Sally, meanwhile, is leaving the party. Even though it's almost midnight, she just can't take it anymore.
As she walks out of the ballroom, Harry bursts in the door.
She steels herself, nose up and defiant as Harry walks right up to her and tells her that he loves her.
She's not having it. She thinks he's just lonely. Confessing his love doesn't erase everything that's happened. Harrumph and phooey.
So Harry channels his inner Cary Grant and delivers the ultimate romantic speech. He names everything he loves about Sally—the fact that she gets cold easily, that she's a persnickety food-orderer, that she gets a crinkle above her nose when she thinks he's crazy, that he can smell her perfume on his clothes, and that she's the last person he wants to talk to when he goes to bed at night.
He wants to spend the rest of his life with her. So there.
Sally's still mad, but she's also clearly touched. She says she hates him, but we know she means the opposite.