Departures and marriages are imminent in Sanditon, although which ones will actually occur remains to be seen.
The Hankins siblings arrive at the Parker household first thing in the morning to offer prayers for Mary, who has fallen unconscious with a fever. Their support is welcome: Dr. Fuchs says Mary requires a miracle to survive. Tom wants to make amends and repent for ignoring Mary’s plans for the old town. Charlotte offers to accompany him there and explain Mary’s thoughts.
The pair visit Mrs. Filkins, Mary’s former maid, and Tom assures her that she will have whatever she needs. She gives him a small crucifix for Mary.
He returns to Mary’s side, pressing the cross into her hand, and tells her she has always been right about the old town. He’ll give up all his plans for her survival. Her eyes open.
Susan and Samuel are sharing a much less fraught morning together on the beach. Samuel tells Susan that he is finally, for once, considering marriage: to her. But after she receives a letter from a soldier on horseback, she returns to Samuel and tells him that they were caught up in the moment, and that they should let it pass and return to their lives.
As Mary recovers in bed, Charlotte tells her that she has called off her marriage to Ralph. Mary urges her to go tell Alexander. But when Charlotte arrives, he is out riding, and she doesn’t want to leave a message, preferring to tell him in person. Samuel tells Charlotte that Susan is leaving Sanditon.
Susan explains to Charlotte that the king, her former lover, has summoned her back to London. She cannot refuse. But she urges Charlotte to find her own love, and Charlotte says she will speak to Alexander at Lady Denham’s wedding to Rowleigh Pryce.
But then Georgiana hears from Lydia that she is engaged. Since Alexander has been courting Lydia, and has decided that Leo and Augusta need a mother, Georgiana and Charlotte assume it is to Alexander. It is too late for Charlotte.
When Charlotte arrives at Lady Denham’s wedding, she urges Samuel not to let Susan leave Sanditon, revealing the reason Susan is going. Augusta—who has not been eating or sleeping since her rejection by Edward—asks Charlotte to sit with her, placing Charlotte awkwardly next to Alexander.
But they’re not there for long. Edward appears and tells the Reverend Hankins and Pryce that Lady Denham will not be coming, despite Edward’s urging—even though he would lose a home if she got married. Edward then announces to the crowd that the wedding is off.
Beatrice Hankins is perplexed that Lady Denham would forestall a chance at happiness at her advanced age. Beatrice argues with her brother over her relationship with Fuchs. Later, her chastened brother asks a beaming Beatrice if she’d like to invite Fuchs for tea.
Samuel tells Susan that the king doesn’t deserve her and that she should stay, but all she can say in response is sorry. She has to go.
Pryce barges in to Lady Denham’s home to speak with her. He has already been disappointed by Tom pulling out of the deal to develop a hotel over the old town, in honor of Mary’s wishes; now he has been left at the altar as well. Lady Denham explains that she decided she couldn’t give up her house, Sanditon, her life, her title, her independence—they were too hard-won.
Agnes Harmon fought hard to find her daughter, Georgiana, but now she has disappeared without a word. Georgiana decides she was just another lying fortune hunter. But then Agnes reappears while Georgiana is having her dress fitted for her wedding to Harry Montrose.
Agnes explains that she left a note, and Georgiana realizes it got lost in a pile of papers. Along with the note is the money Lady Montrose offered Agnes to disappear. Georgiana confronts Lady Montrose in front of her children and gives the money back. Harry follows Georgiana after she leaves and tells her that what his mother did is indefensible. Marrying each other would be a mistake; they’d both be miserable, and they both deserve love.
Georgiana tells her mother she is ashamed of the person she had become, and that she wants to give her fortune to Agnes, to use it for good. Agnes says Georgiana could do that herself, with the help of Otis, who loves her. Agnes’ absence was to visit Otis in London: she had realized that Georgiana was in love with him and not Harry. Georgiana apologizes to everyone for her recent destructive behavior and tells them that she and her mother are going to London to see Otis.
Charlotte has decided she will go stay with her sister Alison for a bit. Her father has forgiven her for calling off her marriage to Ralph, and she wants to teach and open a school for girls.
The Parkers want to include such a school in their plans for the old town, thanks to their benefactor Alexander Colbourne’s insistence on education for women. The plans also include an outdoor plot for each family and repairs to all the decrepit homes. The Parkers approach Lady Denham to invest, even though there will be no financial return. Denham recognizes her similarity as an independent woman to Charlotte, and agrees to match any money that Alexander is donating.
Back in her big manor, Edward assures Lady Denham that he will stay with her to keep her company for as long as she needs. But she has a new plan for him. She promised to provide him a living if she thought he had reformed; his kindness towards her, argument that she should marry even though it would deprive him of a home, and refusal to “ruin” Augusta all speak well of him. So Lady Denham will provide his salary as a clergyman.
Pryce also has a new plan: he has decided to fully finance Tom’s initial plan for a modest hotel that won’t displace anyone, so that Pryce will have somewhere to stay when he comes to visit Lady Denham every few months—if she’ll permit.
Harry and Arthur also reunite, now that Harry and Georgiana are not to be married. Georgiana reunites with Otis in London, telling him that he gave her back her mother, and now her mother has led her back to Otis. They marry, with only Agnes as witness.
Susan never made it to London, having turned around halfway there to return to Samuel. She can’t live without him. The new couple also realize that Charlotte has mistaken information: Alexander is not engaged to Lydia. They rush to Alexander as Charlotte boards a carriage to leave Sanditon.
Alexander hops on a horse and stops Charlotte’s carriage along the cliffs, just as Sidney Parker once did. The ending is happier this time. Alexander explains that Lydia has been carrying on a secret courtship, and is engaged to that man, not Alexander. Both he and Charlotte are at liberty to marry whomever they choose. They kiss—and this time Charlotte doesn’t pull away, crying at the impossibility of their relationship. This time, it’s just the beginning, not the end.
Charlotte and Alexander marry, with numerous happy couples in the crowd: Denham and Pryce, Beatrice and Fuchs, Georgiana and Otis, Samuel and Susan, Tom and Mary, Harry and Arthur. Edward stands in clergy’s robes in back.
A year later, the Parkers have opened a school in the old town, and Charlotte is the teacher. Alexander meets her after school with their infant, and Charlotte assures Augusta and Leo that a girl can be whatever she chooses to be.