A film by Catherine Breillat

Set in 1835 - the century in which Les Liaisons Dangereuses was penned - An Old Mistress is a Parisian tale of lust, longing and the torments of passion.
Victomte de Prony, a dapper aristocrat, loves nothing more than to observe and comment upon the romances of his similarly aristocratic social circle. One day, de Prony pays his friend Vellini (Asia Argento) a visit, armed with some rather disturbing information: her lover Ryno de Marigny is set to marry another woman. While de Marigny is well-connected, his financial standing is dire, thus leading to his betrothal to the young, wealthy Hermangarde.
In spite of her lover's engagement, Vellini is convinced that the decade-long sexual bond she has shared with de Marigny is strong enough to override any marriage and, through a series of flashbacks in which their affair is exposed, director Catherine Breillat whimsically comments upon the age-old divide between love and passion.