At some time in the recent past, a human somehow ended up in Ponyville. It turns out that this person fit in quite well. So much so that Twilight tries to find a way to bring in more. Being Twilight Sparkle, she quickly succeeds and finds a few more humans willing to move in. But now more ponies want their own human friend, so she goes looking for more.
And eventually Twilight finds one that might not quite work out.