Apparently, Edward had come to Barton to ask Elinor to marry him. He left the house so abruptly to get some fresh air, gained confidence, then returned immediately to accomplish his mission. Three hours later, everything is settled, and everyone is immensely happy. Yay!
Edward is happier than they've ever seen him (happier than he's ever been!), and he's genuinely cheerful and open to everyone, especially Elinor.
He explains what happened with his engagement to Lucy – they'd fallen in love as teenagers, but as grownups, they'd grown apart. Part of the problem was that he hadn't had a clear path to employment once he left school, and no companions or friends – really, the only person he was close to as a youth was Lucy, so he had no basis for comparison.
That night, everyone is so excited that nobody can sleep. It's a good kind of excitement, though – that of pure joy and relief.
Marianne can only express her joy through crying, and has no words for her feelings.
Elinor was so excited that even she lost her composure for a moment, before she pulled it together and was able to tell him how much she loves him – still, she's far from the normal calm Elinor we're used to.
Edward stays at the cottage for a week, and he and Elinor spend the whole time enjoying each other's company and planning for the future.
Lucy's marriage to Robert is a topic of much discussion as well – how did it happen? Everyone is mystified.
Edward and Elinor discuss the possibility of plotting on Lucy's part; they decide that she probably began with the best intentions of gaining Robert's good favor for her marriage to Edward, but things changed somewhere along the line.
Edward tells Elinor all about his breakup with Lucy. She'd written him a rather awkward letter, after she and Robert were already married, and requested that he destroy all her letters.
He was horrified by the badness of her writing, but pleased by the content – everyone agrees that all's well that ends well.
Mrs. Ferrars has even got her comeuppance, since the very daughter-in-law she hoped to eliminate by disowning Edward has cropped up again with Robert.
Edward hasn't been in contact with his family since this all happened, and he's not sure what is going to happen.
Elinor realizes that Lucy had meant to deceive the Dashwoods and hurt Elinor in particular by leading Thomas to believe that she had married Edward, not Robert. It's clear that Lucy is not actually a nice girl, but clearly something of an evil one. He wishes he'd known about it before his mother found out about everything – he would have broken up with Lucy had he known her real nature.
He can't imagine why Lucy stuck with him for so long – why would she have stayed with him, even when he was disowned?
Elinor figures that Lucy probably thought that she could gain from the association anyway, and that she'd assumed that in the end his family would give in.
Elinor teases him for spending so much time at Norland with her when he was otherwise engaged with Lucy, but she doesn't mean it. He earnestly defends himself, saying that he thought he was safe from falling in love with Elinor if he was engaged already. Needless to say, he was wrong.
Edward is glad that Colonel Brandon is coming to visit. He's excited to get to know his benefactor better; he used to resent Colonel Brandon because he though the Colonel was engaged to Elinor and he'd assumed that that's why he was offered the job at Delaford. Now that everything's cleared up, though, he's excited to make a new friend.
As for money, Elinor has a thousand pounds of her own, and Edward has two thousand – combined with the Delaford living, that doesn't give them quite enough to live on.
Edward hopes that his mother might change her mind toward him, but Elinor's not so sure. It seems to her that Robert's offensive marriage will just mean that Fanny will get more of the Ferrars fortune.
A few days after Edward arrives, Colonel Brandon shows up. Mrs. Dashwood is overjoyed that everyone's together, but it means that they're out of room at the cottage, and Colonel Brandon has to stay at Barton Park. However, he comes to visit every day.
He's been much revived by his three weeks at home, and is even more revived by Marianne's improvement in health. Mrs. Dashwood tells him all the surprising news about Lucy and Robert, and the Colonel is especially happy that he's helped Edward and Elinor out.
Edward and Colonel Brandon become great friends quickly, not only because they're quite similar in personality, but also because they're in love with two sisters.
Mrs. Jennings sends a letter from town relating the whole story of Lucy and Robert, which Elinor is now able to read with humor, not anxiety.
John also writes, lamenting how unfortunate Mrs. Ferrars and Fanny are. Both Robert and Lucy are in her bad book, and even if she un-disowns Robert, she'll never forgive Lucy.
Mrs. Ferrars hasn't said anything about Edward yet, but John thinks that Edward should write a conciliatory note to his mother – perhaps she will forgive him (and give him some money).
Edward isn't sure what to do and doesn't want to write, as John suggests, a letter of "submission," so Elinor counsels him to write a letter asking for forgiveness, perhaps with a little humility thrown in there for good measure.
Colonel Brandon and Edward leave together to visit Delaford, after which Edward will go to London.