Based on the novel Les Liaisons Dangereuses, Untold Scandal is set in aristocratic 18th-century Korea at the end of the Chosun Dynasty. The irresistible temptress Lady Cho (Lee Mi-Suk) asks her cad of a younger cousin, Jo-won (Bae Yong-Jun), to deflower the innocent young Soh-ok (Lee So-Yeon), who is to become her husband's concubine. But his attentions soon shift to the graceful and aloof Lady Sook (Jeon Do-Yeaon) who lives according to her convictions as a Catholic. Jo-won becomes obsessed with seducing this chaste woman who has remained celibate for nine years since her husband's death. However, it proves to be more difficult than he expected when Chosun's notorious playboy sets out to conquer the most virtuous woman in the land.