The Princess of Cleves by Madame de la Fayette

Mademoiselle de Chartres is a sheltered heiress ("in her sixteenth year", i.e. aged 15) whose mother has brought her to the court of Henri II (a disguised version of the court of Louis XIV) to seek a husband with good prospects, financially and in society. Old jealousies against a kinsman spark intrigues against the young ingenue, and the best marriage prospects withdraw. She accepts her mother's recommendation and the overtures of a middling suitor who admires her, the Prince de Clèves. However, after her marriage, she meets the dashing Duc de Nemours, and the two fall in love, yet do nothing to pursue their affections, limiting their contact to an occasional visit in the now-Princess of Clèves's salon.

The Duc becomes enmeshed in a scandal at court that leads the Princess to believe that he has been unfaithful in his affections. A letter from a spurned mistress to her paramour is discovered in the dressing room at one of the estates. The letter is actually to the Princess' uncle, the Vidame de Chartres, who has also become entangled in a relationship with the Queen. The Vidame begs the Duc de Nemours to claim ownership of the letter, which ends up in the Princess' possession. The Duc has to produce documents from the Vidame to convince the Princess that his heart has been true.