In anticipation of Sir Thomas's return, Tom returns to Mansfield Park. Mary Crawford is now repelled by him and definitely interested in Edmund. Henry Crawford returns to his own estate to take care of some business, and Maria and Julia are pained by his absence. Upon Tom's return, a small ball is held at Mansfield; it is Fanny's first ball.
Tom has brought his friend Yates to Mansfield with him. Yates is dull, constantly telling the story about the amateur theatricals in which he had been taking part at the estate he visited before Mansfield. Unfortunately, the host's grandmother had died and prevented the performance. Inspired by Yates's story, Tom proposes that the group put on a play at Mansfield Park. Everyone is enthusiastic, save Edmund and Fanny. Edmund is opposed to private theatricals and points out that the production could jeopardize Maria's engagement. His objections are ignored, however, and a grand plan is laid out for the construction of a theater in Sir Thomas's room and the billiard-room. Fanny soothes Edmund by pointing out that the plan may be abandoned due to the fickleness of the group and the difficulty of finding a play to suit everyone's tastes. Indeed, the selection of a piece turns out to be difficult; half the group wants a comedy, the other half a tragedy, and a piece is needed which has enough good roles for everyone. Finally, they settle on Lovers' Vows, the piece Yates was to have performed in the prior theatricals. The play is scandalous, as it features illegitimate children and bold declarations of love, and the casting will create some awkward on-stage couples. Passed over in favor of Maria and Mary Crawford for the good parts, Julia refuses to participate in the play.
The rest of the play is then cast. Rushworth is given a small role, and his involvement in the play gives Austen a chance to engage in some comedy; he is an idiot and a fop. Edmund, hearing which play is to be performed, is aghast, but again he is ignored. Mrs. Norris is as excited about the play as anyone, bustling around making preparations for the stage. One part is still uncast, that of Anhalt, the clergyman who ends up married to Mary Crawford's rather sexually aggressive character. Tom tries to get Edmund to take the part; when he refuses, Tom decides to ask a neighbor to participate. He then attempts to get Fanny to take the last uncast female role; when she refuses, she is attacked by both Tom and Mrs. Norris, who call her ungrateful and try to remind her of her place. Mary Crawford comes to her rescue, but Fanny distrusts her friendliness.
While the young people have been engaging in acting all along, Yates's suggestion that they put on the play literalizes some of what's been going on. The play is highly inappropriate, because it is so close to the truth: Maria and Henry will be playing mother and son, and will be forced to play some rather intimate scenes. Acting casts doubt on sincerity and destabilizes the relationships between these individuals; in their behavior towards each other, what is "acting" and what isn't? That the house is physically turned into a theater confirms the powerful influence of acting on the lives of these people. Particularly since we already know that some of these characters are acting on hidden motives (Maria is marrying Rushworth for his money, while trying to get Crawford to declare his love at the same time, for example), anything that calls their sincerity into question is a threat. Acting is also inappropriate for the professional connotations it bears. Edmund speaks of having seen plays performed by professional companies and notes that their performances are perfectly appropriate. For his sisters and his brother, though, to undertake a task that is normally the job of middle-class individuals who learn it as a craft and are then paid for it would be highly inappropriate. Turning the house into a theater is almost like turning it into a commercial establishment, even though no audience will be brought in.
Most importantly, though, this play gives the women a chance to behave in a sexually aggressive manner. Given that this is Maria's and Mary's tendency already, the play is dangerous to a nineteenth-century world. Although they would purportedly be playing a role and not behaving as themselves, the danger and the inappropriateness are still there, and even to pretend that women could behave in such a way is a threat to society.
Fanny and Edmund set themselves apart by refusing to participate. While Edmund has some knowledge of the play and is opposed to the idea of acting in general, Fanny reinforces her opinion with research. She actually reads the play. As she goes through the script, the correlation between intimacies on stage and desired intimacies in real life is immediately apparent to her. In its way, the play is more "real" than the "real" lives of these characters right now; at least the affections displayed on stage will be consistent with the emotions felt in her friends' hearts. Thus, although the production of the play represents a form of public behavior--"acting"--that is inappropriate, it also serves to cast light on the great deal of "acting" going on in the everyday lives of these people. Tom and Mrs. Norris's attack on Fanny demonstrates the blurring of the boundaries between acting and reality. While she has always been aware of her precarious position in the family, Fanny has never been subjected to aggression like this before. Mrs. Norris states Fanny's situation without any of the niceties that normally accompany it. In other words, disoriented by the goings-on onstage, she has stopped acting. Clearly, the play is dangerous in many ways, and Edmund's opposition to the production is logical, even though it can seem priggish.
In some ways, though, Edmund is indeed a prig. Facing the prospect of little or no inheritance as the younger son, he constantly seeks to distinguish himself from his dissolute older brother through his moral behavior. On the one hand, this allows Austen to criticize the rigid English system of inheritance. Protected by convention and to some extent by law, Tom is allowed to behave as badly as he pleases, knowing that he is guaranteed to become master of Mansfield Park at his father's death. Edmund is the better person, but he must take up a profession. Edmund's priggishness also shows his humanity, though. He is not perfect, and despite his role as teacher to Fanny, he is still in need of some education himself. Only when he has learned as he is supposed to will Edmund be able to achieve happiness. Until then, he relies on a stilted moral code to guide the family.
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.