Incest

When the
immoral libertine Monsieur de Franval marries and fathers a daughter, he
decides to inculcate in her a sense of absolute freedom, an unconventional
education that involves the two becoming secret lovers. But Franval’s
virtuous, God-fearing wife becomes suspicious and confronts him, setting off
a tragic chain of events.

Part of Sade’s The Crimes of Love cycle, this shocking tale - which was
among the writings banned for publication until the twentieth century - tests
the limits of morality and portrays the disastrous consequences of freedom
and pleasure.