Forbidden Quest (Korean: 음란서생; RR: Eumranseosaeng) is a 2006 South Korean period drama film about a scholar during the Joseon period who begins to write erotic novels, and becomes the lover of the King's favorite concubine.

At the start of the film, Kim Yoon-seo, an Inspections officer (police inspector) is seen at his home where his brother has been beaten almost to death.

Jung-bin is in turn impressed by Yoon-seo's knowledge on the subject and invites him to talk to her some more about art some day.

Yoon-seo teams up with Lee Gwang-hun, an inspector who likes to torture people in his dungeons, to try to hunt down the culprit.

He is at first outraged by the content (pornography being illegal at the time), but when the old man says the whole city is waiting for the book he shows some interest and perhaps embarrassment about never having heard of the author.

When a bee lands on her he violates all protocol risking his death, by going beyond the curtain and brushing it off her shoulder.

The illustrator has trouble understanding some of the things he is supposed to draw, so next time Yoon-seo meets Jung-bin, he has him hide behind a wall, and spy on them while they have sex.

Gwang-hun wishes to stop but Jung-bin decides to call the matter to the King's attention.

They tie Yoon-seo to a contraption, and Gwang-hun turns the handle until the bones of his legs snap in half.

In the end he is beaten but is forced to leave with the people from the shop while the eunuch takes Yoon-seo back to his jail.

Gwang-hun is left alive because Yoon-seo threatens to claim the eunuch as the illustrator, which would be possible because he did come with Jung-bin to all their meetings.

The King tells the servant to castrate him and make him a eunuch so he may be with Jung-bin for the rest of his life, even though the operation may kill him due to his age.

The King is overcome by anger and grief, as he was most in love with her, and at first wants to personally kill both Jung-bin and Yoon-seo.