Untold Scandal is a 2003 South Korean romantic drama film directed by E J-yong, and starring Bae Yong-joon, Jeon Do-yeon, and Lee Mi-sook. Loosely based on the 1782 French novel Les Liaisons dangereuses, this adaptation takes place in late 18th century Korea, during the Joseon dynasty.
In Korea the film was given an R-18 rating by the Korean Film Ethics Commission. The film was a major commercial success, and became the fourth highest grossing domestic film of 2003 with 3,522,747 tickets sold nationwide.
A beautiful but cynical and manipulative noblewoman makes a bet with her free-spirited womanizing cousin that he can have sex with her if he is able to seduce a young woman of great virtue. He accepts the challenge with enthusiasm though not suspecting the nasty trap he is walking into.
(Summary from Wikipedia)