Charlotte Heywood is unmarried and still lives at home, the eldest of the Heywood daughters to do so. Her father is a country squire, a gentleman, and the family lives in the south-east of England in the pretty, coastal county of Sussex. It is a usually quiet place to live, which is why it is so remarkable when Mr and Mrs Parker or Sanditon have an accident at the top of the hill near the Heywood home; the carriage they are riding in topples over, and Mr Parker is injured. The Heywoods invite them to spend the night in their home, so that Mr Parker can rest, and so that their damaged carriage can be repaired.
The Parkers end up staying for two weeks; during this time, Mr Parker's chief topic of conversation is his beloved home town of Sanditon. It used to be a tiny dot on the map, a fishing village known only to its inhabitants, but over the past couple of years, Mr Parker and his business partner, Lady Denham have been trying to turn Sanditon into a fashionable vacation spot. Mr Parker is particularly proud of the bathing machines he has installed so that people can change into their swimwear and wade into the ocean. He has also had a new home constructed for his family, and they enjoy their own personal bathing machine there.
The carriage is eventually repaired, as is Mr Parker's injured foot, and so the Parkers return home to Sanditon, taking Charlotte with them as their guest for the summer. As soon as they arrive, Charlotte wastes no time in becoming acquainted with the town's inhabitants, starting with Lady Denham, who has been widowed twice and is extremely rich. She inherited her title from her second husband and has taken in her niece Clara Brereton. Clara is a very sweet young lady, and is extremely attractive, but she has no money, which is why her aunt has taken pity on her. Clara is also the only member of the extended Denham family not actively seeking a portion of Lady Denham's wealth; this is more than can be said for Edward Denham and his sister Esther, her nephew and niece by marriage.
Charlotte settles in quite quickly and soon receives a visit from Mr Parker's siblings, two younger sisters, and a younger brother. All three claim to be invalids, but Charlotte believes that they are making up their ailments because they seem to be able to get around very well, and they have a great deal of energy for people in poor health. Diana, one of the sisters, is in Sanditon on a mission for a wealthy family who currently live in the West Indies; it later transpires that nobody has actually asked for her help, but she has inserted herself into their business and is determined to maintain the relationship. She also has news that excites Mr Parker in particular; a large group of visitors from a girls' school are heading to Sanditon for the summer.
Diana's information has been vague, to say the least. When the party from the school arrives, it becomes clear that they and the family from the West Indies are the same entity. They are a party of three; Miss Lambe, a rich young heiress, and the Beaufort sisters, rather common English girls. Lady Denham quickly dismisses the latter but wants to be introduced to Miss Lambe, because she is wealthy, and would make a suitable wife for her feckless nephew Edward.
Sidney Parker, the second eldest of the Parker siblings, arrives without warning to await the arrival of two friends who will be staying with him. Charlotte is attracted to him and there is a definite frisson between them.
Charlotte accompanies Mrs Parker to Lady Denham's home, where she notices Clara huddled up conspiratorially with Edward, as she contemplates the meaning of the placement of the portraits of Lady Denham's former husbands; Sir Henry Denham's portrait hangs in pride of place above the fireplace, but her first husband, who actually owned the home she still lives in, is relegated to a miniature in the corner of the room.
