Today's summary is short because in this mid-length chapter, precious little happens.
Oh Mrs. Jennings! I love you and your babbling about possible Things Gone Wrong for Colonel Brandon. And how each and every completely different one seems equally probable to her.
Meanwhile, Elinor is wondering about a different sort of mystery. She's pretty sure that Marianne and Willoughby are engaged, and she can't figure out why they aren't announcing it. She wonders so very much, in fact, at why no announcement has been made when neither of them seems particularly secretive or bound by convention, that she begins to suspect that maybe Marianne is not engaged to Willoughby, so she doesn't want to ask.
Still, Willoughby spends nearly all his time with Marianne, most of it at Barton Cottage. He seems so attached to Marianne and her family that his attachment extends to their residence, and he opposes any suggestions of change/improvements and declares his affection for all of them (with particular focus on Marianne).