The narrator fills in some details for us. How could Becky and Rawdon have gotten married? Easy enough – they are both of age, so they slipped off and just did it one day. It might not have been Rawdon's best decision, but probably his most honorable. After all, isn't that what men are supposed to do – meet a girl, fall in love, then make it legal?
Rawdon is happy to leave all the details of their future in his wife's hands. He is at least smart enough to realize that she has a much better head on her shoulders than he does.
While Becky is dealing with things, Rawdon rents an apartment for the two of them in a middle-class London neighborhood.
That night Becky is playing it to the hilt. She sings, tells stories, plays cards – everything possible to make Miss Crawley happy.
The narrator drops in to let us know that if Rawdon had been there that night, and if he and Becky had confessed, Miss Crawley would have instantly forgiven them. But then we'd have no novel.
As it is, the next morning, a maid named Betty Martin finds a note addressed to Briggs on Becky's bed, which has clearly not been slept in.
Becky's letter tells Briggs that Rawdon is her husband, and that Becky has gone to be with him.
Right at that moment, Mrs. Bute comes to Miss Crawley's house (Firkin had written her a letter, remember?).
Briggs tells Mrs. Bute the news, and together they very slowly, suspensefully, with as much freaking out as possible, tell Miss Crawley.
She totally loses it.
Sir Pitt then comes to the house to pick Becky up and take her back to Queen's Crawley.
Briggs tells him that she is married to Rawdon and he really flips out. He is beyond jealous of his son (nice little Oedipal reversal there), storms back home, and trashes her room and all her stuff.