Sir Thomas is scheming. He needs a way to make Fanny miss Henry.
Sir Thomas has trouble reading Fanny since she's just so gentle all the time, and isn't very forward about what she's really thinking or feeling.
Edmund is also confused that Fanny doesn't really seem to miss the Crawfords all that much. He thought she and Mary were BFFs.
Meanwhile, Edmund seems to have lost all his doubts about Mary and is determined to marry her now.
Fanny decides that Mary has blinded Edmund to all of her faults and feels depressed about the prospect of them indeed marrying.
In other news, William is coming back to Mansfield for a visit, and Fanny is thrilled to see him.
Sir Thomas gets an idea: he decides that Fanny should go back to Portsmouth with William and see the rest of her real family for the first time in years.
This seems random but it's really quite crafty: Sir Thomas thinks that if Fanny has to live with her dirt poor real family for a while she'll appreciate the kind of fabulous lifestyle that Henry and his money can offer her, and then she'll quickly accept Henry.
Fanny is really eager to see her family again and she and William plan their trip excitedly.
But Fanny is also sad to be leaving Edmund for two whole months, especially since he'll probably be engaged by the time she returns. But she decides it might be good to get some distance from Edmund, too.
Sir Thomas convinces Lady Bertram to let Fanny go.
Fanny has high hopes for her family reunion and expects that she and her mother will grow close.
But then Mrs. Norris decides that she might like to take a road trip (since Sir Thomas is paying for it) and wants to crash William and Fanny's party. They're horrified.
But then Mrs. Norris realizes she'll have to pay her own way back to Mansfield Park and decides to stay home. Crisis averted.
Edmund was planning to go to London to see Mary but he delays his trip since Fanny will be gone and he doesn't want to leave his parents completely alone.
He promises to update Fanny on his engagement status and Fanny isn't happy to even think about it.