Lady Susan

Lady Susan is an early epistolary novel (novel in letters) by Jane Austen. It tells the story of an unscrupulous coquette (flirtatious woman) widow who does not care about the feelings of other men. She wrote it when she was writing her first version of "Sense and Sensibility" (which was at that time called "Elinor and Marianne"), and which was also at first, like "Lady Susan", written in letter form. She was at this time 20 years old.
Style.
The epistolary novel had been popular in the 18th century, but it was not the best style of writing for Jane Austen's talents (which is why all her major novels were written in the third-person narrative style). She admired Richardson very much (all of his books are written in letters, like "Pamela (novel)" and "Clarissa (novel)"), and she also admired Frances Burney's style, but none of their styles came naturally to her. She pointed out at the end of "Lady Susan": "This correspondence (letter-writing), by a meeting between some of the parties (people) and a separation between the others could not, to the great detriment of the Post Office...be continued longer."
In those days, girls spent some time each day especially to write letters, so a story through letters is much more realistic than it would be today. People like Frances Burney wrote letters that were witty and full of information, so that her diaries and letters were later published. The letters of William Cowper, too, are famous. Jane Austen's letters, however, are private letters about family matters, such as sick babies, partners at balls, beef, and raspberry bushes.
Plot Summary.
Lady Susan Vernon is a beautiful and charming(someone who can please and attract someone else)recent widow. She visits her brother-in-law and sister-in-law,Charles and Catherine Vernon, with little prior notice at Churchill, their house. Catherine is not happy, as Lady Susan, a long time ago, had tried to prevent her marriage to Charles. Catherine's unwanted guest has also been described to her as "the most accomplished(very skilled in something) coquette(a flirtatious woman) in England". 
Catherine's brother Reginald arrives a week later, and despite Catherine's strong warnings about Lady Susan's character, soon falls in love with her. Lady Susan toys with(to think about something not very seriously)the younger man's affections for her own enjoyment. Later, because she thinks it makes her sister-in-law, Catherine worried. She writes to her confidante(someone who you trust with your secrets), Mrs. Johnson. Mrs. Johnson recommends Lady Susan to marry Reginald, but Lady Susan considers him to be not as good as Mr. Manwaring, whom she flirts with. 
Frederica, Lady Susan's 16-year-old daughter, tries to run away from school when she learns of her mother's plan to marry her off to a rich but dull man, she does not like. The man is Sir James Martin. She then also becomes a guest at Churchill. Catherine comes to like her, and finds out that her character is unlike her mother's. As time goes by, she detects Frederica's growing attachment to the oblivious(not aware of about what is happening around someone) Reginald.
Later, Sir James Martin shows up uninvited(arriving somewhere without being asked to), which makes Frederica unhappy. Lady Susan is annoyed by this. When Frederica begs Reginald for support. She had been forbidden by Lady Susan to ask Charles and Catherine. This causes a disagreement between Reginald and Lady Susan, but the Lady Susan soon repairs the relationship.
Lady Susan decides to return to London and marry her daughter off to Sir James. Reginald follows, still in love with her and intent on marrying her, but he encounters Mrs. Manwaring at the home of Mr. Johnson and finally learns Lady Susan's true character. Lady Susan ends up marrying Sir James herself, and allows Frederica to live with Charles and Catherine at Churchill, where Reginald De Courcy could like her too.