The chapter opens with Mr. Casaubon's letter to Dorothea, proposing marriage. It sounds very formal and official. No compliments, no flattery, and nothing lovey-dovey.
Dorothea likes it, though, and she's ecstatic at the idea of being able to love and serve someone who needs her help (Mr. Casaubon basically just needs a secretary). A whole new world of knowledge seems to be opening before her! Hurray, helping a crusty old scholar organize his notes!
Dorothea writes back almost immediately, accepting his offer in a few lines.
She gives her letter to her uncle to mail for her, and he expresses some surprise and concern – especially on Sir James' account.
Celia guesses what must have happened when she sees Dorothea blush at the mention of Mr. Casaubon's name at breakfast, but she can't believe it.
She decides to test her theory, and makes a few lightly insulting remarks on the way Mr. Casaubon eats his soup.
Dorothea cuts Celia off, and says that she's engaged to marry him.
Celia is appalled at the thought of her sister marrying that old man with the moles who eats his soup so noisily, but she keeps her horror to herself.
Mr. Casaubon comes to dinner and afterwards has a talk with Dorothea about their upcoming marriage.