The chapter opens with Emma thinking about Mr Knightley, and
Long story short, Harriet and one of her friends were approached by gypsy children looking for a handout, the friend did a runner and Harriet . . . didn't. I confess that the Keystone Kops-like description of Harriet, trying to scramble up the bank but failing, cracks me up every single time I read it. But I digress.
What with Harriet being easy pickings, the gypsies went for the full-court press, begging for additional money past the shilling she handed over, and Frank arrived and chased them off. The story can be told with additional flourishes, as I'm certain Emma did for her nephews and absolutely everyone else in Highbury did as among themselves, but to cut to the chase, the chapter ends (more or less) with Emma (mentally) chanting "Frank and Harriet, sitting in a tree . . . "
I cannot let this chapter pass, however, without commenting on this particular line: "How much more must an imaginist, like herself, be on fire with speculation and foresight!--especially with such a groundwork of anticipation as her mind had already made."
To be an imaginist is quite a thing, don't you think? It's how Austen describes Emma here, which comports well with what we know of her. But the term applies equally well to authors in general, and to Austen in particular. Just as Emma seeks to create characters (by building Harriet Smith up, say) or to write stories (through match-making), so Austen creates characters and writes stories. No wonder Austen liked Emma so much - and worried that nobody else would do so.