Turns out Edward Ferrars and Lucy Steele have been secretly engaged, and Fanny Dashwood completely flipped the shit when she found out. The description of the antics at the Dashwoods' house is hilarious, and is extremely reminiscent of things from Austen's juvenilia. I offer the following into evidence.
From Sense & Sensibility:
. . . poor Nancy, who, you know, is a well-meaning creature, but no conjurer, popt it all out. 'Lord!' thinks she to herself, 'they are all so fond of Lucy, to be sure they will make no difficulty about it;' and so, away she went to your sister, who was sitting all alone at her carpet-work, little suspecting what was to come--for she had just been saying to your brother, only five minutes before, that she thought to make a match between Edward and some Lord's daughter or other, I forget who. So you may think what a blow it was to all her vanity and pride. She fell into violent hysterics immediately, with such screams as reached your brother's ears, as he was sitting in his own dressing-room down stairs, thinking about writing a letter to his steward in the country. So up he flew directly, and a terrible scene took place, for Lucy was come to them by that time, little dreaming what was going on. Poor soul! I pity her. And I must say, I think she was used very hardly; for your sister scolded like any fury, and soon drove her into a fainting fit. Nancy, she fell upon her knees, and cried bitterly; and your brother, he walked about the room, and said he did not know what to do. Mrs Dashwood declared they should not stay a minute longer in the house, and your brother was forced to go down upon his knees too, to persuade her to let them stay till they had packed up their clothes. Then she fell into hysterics again, and he was so frightened that he would send for Mr Donavan, and Mr Donavan found the house in all this uproar. The carriage was at the door ready to take my poor cousins away, and they were just stepping in as he came off; poor Lucy in such a condition, he says, she could hardly walk; and Nancy, she was almost as bad. I declare, I have no patience with your sister; and I hope, with all my heart, it will be a match in spite of her. Lord! what a taking poor Mr Edward will be in when he hears of it! To have his love used so scornfully! for they say he is monstrous fond of her, as well he may. I should not wonder, if he was to be in the greatest passion!--and Mr Donavan thinks just the same. He and I had a great deal of talk about it; and the best of all is, that he is gone back again to Harley Street, that he may be within call when Mrs Ferrars is told of it, for she was sent for as soon as ever my cousins left the house, for your sister was sure she would be in hysterics too; and so she may, for what I care. I have no pity for either of them.And here's an example from Love and Friendship:
From this Dilemma I was most fortunately relieved by an accident truly apropos; it was the lucky overturning of a Gentleman's Phaeton, on the road which ran murmuring behind us. It was a most fortunate accident as it diverted the attention of Sophia from the melancholy reflections which she had been before indulging. We instantly quitted our seats and ran to the rescue of those who but a few moments before had been in so elevated a situation as a fashionably high Phaeton, but who were now laid low and sprawling in the Dust. "What an ample subject for reflection on the uncertain Enjoyments of this World, would not that Phaeton and the Life of Cardinal Wolsey afford a thinking Mind!" said I to Sophia as we were hastening to the field of Action. She had not time to answer me, for every thought was now engaged by the horrid spectacle before us. Two Gentlemen most elegantly attired but weltering in their blood was what first struck our Eyes--we approached--they were Edward and Augustus--. Yes dearest Marianne they were our Husbands. Sophia shrieked and fainted on the ground--I screamed and instantly ran mad--. We remained thus mutually deprived of our senses, some minutes, and on regaining them were deprived of them again. For an Hour and a Quarter did we continue in this unfortunate situation--Sophia fainting every moment and I running mad as often. At length a groan from the hapless Edward (who alone retained any share of life) restored us to ourselves. Had we indeed before imagined that either of them lived, we should have been more sparing of our Grief--but as we had supposed when we first beheld them that they were no more, we knew that nothing could remain to be done but what we were about. No sooner did we therefore hear my Edward's groan than postponing our lamentations for the present, we hastily ran to the Dear Youth and kneeling on each side of him implored him not to die--. "Laura (said He fixing his now languid Eyes on me) I fear I have been overturned." I was overjoyed to find him yet sensible. "Oh! tell me Edward (said I) tell me I beseech you before you die, what has befallen you since that unhappy Day in which Augustus was arrested and we were separated--" "I will" (said he) and instantly fetching a deep sigh, Expired --. Sophia immediately sank again into a swoon--. My grief was more audible. My Voice faltered, My Eyes assumed a vacant stare, my face became as pale as Death, and my senses were considerably impaired--."If Sense and Sensibility resembles the juvenilia, it's no coincidence - the first epistolary version was written not long after Love and Friendship, so some of Austen's youthful exuberance and love of the ridiculous is more plain than in the "mature" works (Mansfield Park, Emma, and Persuasion, all written when Austen was in her late 30s and early 40s).
I like that Mrs. Jennings sees no impediment to the marriage - of course, her own husband made his money in trade, and her daughters married well because they came with large dowries, so she can be expected to be more accepting of social inequities. I especially like that she thinks Fanny Dashwood and Mrs Ferrars can go hang, for all she cares. (Not her exact words, but close enough.)
Returning to a recurring theme here: Poor Elinor! Now she has to deal with all the public fallout. But first, she has to tell Marianne. As you might guess, this will not go well. First Marianne is ready to throw Edward under the bus (so to speak), which Elinor has to talk her out of, and then Marianne is all set to believe that Elinor never really liked him all that much - which is not at all the case. In the end, we're left with Marianne realizing that Elinor has been seriously unhappy, and promising to try hard not to make a scene - something put to the test when she has to listen to Mrs Jennings praise Lucy, but Marianne manages it. Finally, Marianne has gotten herself under control, at least a bit.
Poor, POOR Elinor As if the horror of listening to Mrs Jennings weren't bad enough, Mr John Dashwood turns up to discuss things. Mrs Ferrars turns out to be every bit as horrible as you might expect - she tried to pay Edward off so he'd dump Lucy and marry Miss Morton. Failing that, she disowns him. John Dashwood has taken her part, of course, and seems to think that Mrs Ferrars was somehow "liberal" in any of her dealings.
Let me say again how very much I love Mrs Jennings. She calls John Dashwood on some of his crap (as much as one can do and not be completely impolite), then clearly indicates her support for Edward - praising him for being a man of his word and saying he's deserving of praise and support. In fact, she wishes she could find him and ask him to come stay at her house because she feels badly that he's in dire straits and has to pay for lodging and meals somewhere.