Game of Seduction (1976)

Charles is wealthy, a French venture capitalist in the 1830s; he's also an aristocratic assassin, prompting duels for political, monetary, and sexual gain. At his aunt's, he meets Madame Mathilde LeRoi, a virtuous and beautiful woman, and he determines to seduce her. Along the way, his lust and game playing give way to love. One of his partners in crime and seduction, a decadent marquise, determines to break Mathilde's spell over Charles, sending her a forged letter that begins a spiral of tragedy.