Sir Thomas's unexpected return leaves everyone scrambling. They try to present the theatricals to him in the best light, but he is clearly disapproving. Exhausted by his trip, Sir Thomas wants to be alone with his family. He hurries Yates's departure and would even banish Henry and Mary Crawford, although his family prevents this. Sir Thomas greets Fanny with particular kindness, which surprises and pleases her. He is impressed with her adult beauty and demeanor. Edmund gives his father a further good account of Fanny, telling him that she was the only one to oppose consistently the performance of the play. Mrs. Norris takes the first opportunity to remind Sir Thomas of all that she has done for the family in his absence, including arranging Maria's engagement. Sir Thomas, repelled by the woman's manner and not particularly impressed with Rushworth, rebukes her for not having prevented the theatricals. Henry Crawford pays a last visit to Mansfield Park, then leaves for Bath. With Sir Thomas back in charge, Mansfield becomes a more sober place, to the horror of some and the delight of others.
Edmund again speaks to Fanny of Mary Crawford's fine qualities. In the meantime, Sir Thomas has become quite concerned about Maria's marriage to Rushworth. It is apparent that the man is an idiot and that Maria is not particularly fond of him. Sir Thomas offers Maria an out, telling her that he will break the engagement for her. Bitter at Henry's departure, Maria reassures him that she does in fact want to marry Rushworth. The couple is quickly married and departs for Brighton (a fashionable resort town), accompanied by Julia.
With both of the Bertram daughters gone, Fanny becomes the favorite at Mansfield, indispensable to Lady Bertram, of whom she has become rather fond, and beloved by her uncle. Soon she becomes a favorite at the Grants' home too, where Mary Crawford is still staying. After she is forced to take refuge there one rainy day, Fanny becomes friendly with Mary. Soon Mary is dropping hints as to her feelings for Edmund; Fanny is conflicted and keeps quiet. Mary again damages her own case with Edmund, however, by making thoughtless comments about wealth and his choice of careers. The high point of Fanny and Mary's new friendship comes when Fanny is invited to dine at the Grants' along with Edmund. Mrs. Norris and Lady Bertram are stunned, but Sir Thomas intervenes and presses Fanny to accept the invitation. Mrs. Norris uses the occasion for another stunningly cruel diatribe on Fanny's "place" in the family, and even tries to prevent Sir Thomas from sending the carriage for Fanny.
To the cousins' surprise, Henry Crawford is at the dinner, having just arrived from Bath. Henry makes several suggestive comments about Maria and Julia, which annoy Fanny. He also criticizes Sir Thomas for stopping the theatricals; Fanny responds to his criticisms of her uncle with a strong rebuke, which seems to impress Henry. Henry and Mary then have a private discussion of Edmund's financial situation as his father's younger son; it is clear that Mary takes a personal interest in the situation. As the evening wears on, Mary becomes more and more piqued at Edmund's lack of interest in wealth and fashion.
Sir Thomas's return introduces a host of conflicts into the text. He brings a traditional family structure back to Mansfield. His doings in Antigua, however, hint at a possible larger conflict. Fanny explicitly asks him about the slave trade one evening, and, while Fanny would never ask a hostile question, the reference is telling. Britain had prohibited trade in slaves in the empire in 1807, but Caribbean slaves in British territories were not freed until 1834; this novel falls right in the midst of the period of greatest controversy over slavery. Sir Thomas is clearly involved in a morally-conflicted business, and this has caused him to re-examine his own life. The rot has spread from his business interests to his family, as the behavior of his elder son and his daughters shows. In a way, too, Fanny has something in common with the Antiguan slaves. She is given her room and board but is expected to work for them, and her time is not her own. If Lady Bertram needs her, she must stay with her; she is not free to accept an invitation on her own behalf. Sir Thomas's new fondness for Fanny, which leads him to intervene on her behalf, can perhaps be interpreted as his attempt to right the wrong at least in his own family. Given that family was, in the 19th century, often described as a microcosm of the British Empire, Sir Thomas's political maneuverings in his household may be almost radical. However, behind his benevolence to Fanny still lies the fact of his slaveholding, and Fanny's questions about it are not well-received.
With Maria and Julia gone, too, Fanny is finally being treated as a daughter to the family. While Fanny has become an attractive young woman, she is also being manipulated for the purposes of others. Mary Crawford's repellent side comes out clearly in these chapters. She is in love with Edmund, but she does not mean to have him as a poor country parson; she wants to see him change his mind about his career--hence her comments about money being the best recipe for happiness. While she may just seem obnoxious when she says things like this, Mary is actually articulating the reality behind a good many things in life at Mansfield Park. She is certainly describing Maria's marriage perfectly.
Sir Thomas's concern about Maria's marriage reflects a new attitude toward relationships between men and women. While previously marriages among the upper classes had mostly been business arrangements, the early nineteenth century saw a new interest in marriages as companionate relationships: the man and the woman should be not only financially but also spiritually helpful to one another. The harrowing trip Sir Thomas has had to make in the name of business has clearly taught him something about the importance of family and relationships, and he does not want to see his daughter make a mistake. We also know that, despite her neuroses and illnesses, Lady Bertram and Sir Thomas actually have a fairly loving relationship; initially, their match was a bit controversial, but they were in love, and we see Lady Bertram's genuine happiness upon Sir Thomas's return from Antigua. Nevertheless, financial matters cannot be ignored completely, and marriage decisions will continue to be a source of turmoil for the family. Sir Thomas's wish to see Maria marry for affection speaks to his essential wisdom and good intentions, despite his many faults.
Regarding Maria Bertram and Mrs. Norris in the last chapter, neither leaves England. When Austen writes that "an establishment [is] being formed for them in another country," she does not mean continental Europe. Here, "country" simply means another part of the same country (most likely somewhere in the countryside). They are still in England.