The planned excursion ends up not happening at all – we start the chapter with everyone gathered, ready to go.
Colonel Brandon receives an urgent letter and rushes off dramatically.
He returns, and promises that there's nothing wrong. Nobody believes him, and they all pressure him into revealing the contents of the letter. He refuses.
Unfortunately, Colonel Brandon's mystery letter claims that some "business" requires him to go to town (that is, to London). This means that nobody can go to Whitwell, his brother-in-law's estate.
Everyone is totally bummed, and Willoughby snarkily comments to Marianne that Colonel Brandon probably called off their trip because he hates having fun.
Mrs. Jennings keeps prying the whole time, trying to figure out what's wrong with Colonel Brandon (even though it's totally none of her business – or maybe because it's none of her business).
Colonel Brandon goes off on horseback after saying his goodbyes to everyone. It seems like he might be gone to London for a long time.
After he leaves, Mrs. Jennings smugly informs everyone that she's sure she knows what the business is about – it must be something regarding a certain Miss Williams, the Colonel's "natural daughter" (meaning his illegitimate daughter). We're not sure how reliable her information is.
Sir John decides that everyone should have a great day anyway – they decide to go on a drive, and explore the countryside. Marianne and Willoughby go together, of course.
The Middletons throw an impromptu dinner party, and Mrs. Jennings hassles Marianne and Willoughby about their private drive in the morning. She implies that they actually went to Willoughby's aunt's house, Allenham, instead of driving around the countryside as they said they did. Apparently, they walked through the grounds and all through the house.
Elinor can't believe that this happened – after all, Marianne doesn't know Mrs. Smith, Willoughby's aunt, at all.
The two sisters have a little spat over this; Marianne doesn't think that she's done anything wrong. Furthermore, she argues, if it had been wrong, she would have felt it, and wouldn't have had a good time.
Marianne ponders the situation and admits good-naturedly that perhaps it wasn't the most proper thing to do. However, she cheers up just thinking about the idea that it might be her house with Willoughby one day, and goes on to describe its charms to her sister.