The narrator has just attended a funeral, and he's sick of doing the hand-shaking and polite conversation that one does at such a function. Who can blame him? So he's driving the country roads of Sussex—the place where he grew up—to kill time.
Before he even realizes what he's doing, he drives to his childhood home. It feels weird to him.
He's supposed to be driving to his sister's house where people are waiting for him, but they're just going to ask him a bunch of questions about stuff he doesn't feel like answering. How's his marriage? Failed ten years ago. How're the kids? Grown up and distant. The usual.
Instead he drives to the Hempstock Farm at the end of the lane.
The door's unlocked, so he just lets himself in. That's pretty presumptuous.
Inside the dim interior there's a really old woman with long gray hair. She remembers him, but can't place the face until he reminds her the last time he was there she gave him warm milk from the cows, when he was about seven years old. Oh right—he was Lettie's friend.
The old woman offers him tea, but he asks to go down to the duck pond. Lettie called it the sea, or something but, you know, she's old.
Sure enough, there it is: the pond. It's smaller than he remembers. And maybe he and Lettie had fallen in? Can't really remember. Where'd she go again? Australia? Somewhere far away.
But then after all the stream-of-consciousness, he remembers that Lettie called it the ocean. And all of a sudden, he remembers everything.