Secret Door — Season 1

After witnessing raids on commoners to deal with the illegal book distribution, Lee Sun is doing his best to legalize books. Refusing to drink medicine, King Young Jo says he is going to abdicate.

The Soron and Noron are fighting against each other for the right to investigate after Shin Bok's dead body has been found. However Lee Sun decides different and orders Gye Hee to investigate.

Unable to believe Gye Hee's report, Lee Sun orders for a re-investigation of Heung Bok's murder case.

To find the truth behind Heung Bok's murder case, the Crown Prince sneaks Ji Dam out of the palace to avoid suspicions from the Crown Princess. Meanwhile, the Crown Prince decides to conduct a secret investigation with Ji Dam…

The Crown Prince asks Ji Dam's father for permission so that Ji Dam can help him on his secret investigation. Meanwhile, after taking another closer look at Heung Bok's suicide letter the Crown Prince and Ji Dam conclude that it is not Heung Bok's handwritting....

Being afraid of Ji Dam' being chased by the police, her father asks the geishas to turn her into a geisha temporarily. Meanwhile, Kim Taek finds out that the written pledge in his possession is fake…

The Crown Prince gets more suspicious about the murder case and tests the Norons making the Noron members very uneasy. Meanwhile, Ji Dam is shocked by a conversation she overhears...

The Crown Prince with a heavy heart orders a search on his Master's house for the Heung Bok's crime. He reveals that his Master was hiding the missing book from the night of Heung Bok's murder in his home…

The king asks the Crown Prince why he went to go see Kang Pil Jae on the night he was murdered but the Crown Prince does not respond. There is evidence against the Crown Prince so the king confines him to his quarters. Meanwhile, the Crown Princess does something unexpected to Ji Dam...

Ji Dam asks for the Crown Princess' permission to help the Crown Prince on the investigation. Ji Dam helps in trying to find the culprit who killed Kang Pil Jae. Meanwhile, the king commands Kim Taek to bring the culprit who switched the written pledge while Kim Taek tries to make a deal in getting the real written pledge back...

The Crown Prince tries to find the identity of Juk Pa by convincing the Sorons to impeach Kim Taek. Meanwhile, Kim Taek tries to convince the king that the Crown Prince knows about the written pledge and that it's time to enthrone a new heir...

The king warns the Crown Prince about letting his true feelings show to others if he wants to hold onto the title of Crown Prince. Both the Norons and the Sorons are nervous about how the Crown Prince has been acting. Meanwhile, the king is angry about a book that has been circulating in the palace.

The king is convinced the book was created by the Sorons, so he arrests everyone in the party and Kim Taek starts a dangerous rumor. Meanwhile, the king gets an unexpected offer.

The king takes away the Crown Prince's rights. Three years pass, the Crown Prince asks Kim Taek to teach him and become his new master. Meanwhile, the Crown Prince spends his time with the children of Noron at with geishas and unexpectedly runs into Ji Dam.

The Crown Prince's secret basement has been revealed. Soon the Crown Prince will have to meet the ambassadors from Qing. Meanwhile, the king calls the members of the Noron party to the palace to talk about foreign affairs regarding the Qing.

Kim Taek has been trying to select a new Crown Prince. The Crown Prince sets a trap for Kim Taek. Meanwhile, Kim Taek goes behind the Crown Prince's back to try to get help from the Qing in bringing down the Crown Prince, trying to start a war.

The king has been suffereing from nightmares but after realizing the Crown Prince's true plan he reinstates the Crown Prince back into politics. Meanwhile, Eunuch Jang's brother has been arrested for taking the civil service exam under a false name.

Na Chul Joo asks the Crown Prince if he is willing to attack his father. The Crown Prince is conflicted all while trying to keep his promise to the people. Meanwhile, the king is being persuaded to take a new queen...

The king commands that the civil service exam be stopped. While the soliders are suppresing the people, citizens arrive at the scene. Meanwhile, the king tries to get the Crown Prince to blame his crimes on someone else so that the king won't have to punish his son.

The king will hold a selection process in finding the new queen. Meanwhile, the Crown Prince tries to keep his promise by building a secret library in the northwestern region for the commoners who weren't allowed to take the civil service exam.

The Crown Prince finds out that Na Chul Joo is planning on assassinating the king. Meanwhile, Hong Gye Hee grows suspicious of the Crown Prince and does everything he can to find evidence against him. The king is also made aware that the Crown Prince has been taking money out of his personal savings...

Hong Gye Hee goes against the king's command when handling the Crown Prince's personal savings. Meanwhile, in a drunken state the Crown Prince reaches out to Lord Min to contemplate his heavy decision.

The king finds out about the secret library that the Crown Prince has created and the basement library in his quarters. The king thinks that the Crown Prince was plotting against him. Meanwhile, Na Chul Joo decides to go ahead with the assassination plan even though the Crown Prince has asked him not too...

The king commands the Crown Prince to pass his crimes to Lord Min's son so that the Crown Prince will avoid death. Lord Min asks for his resignation in order to save his son's life. Meanwhile, Na Chul Joo and his soldiers sneak into the palace to carry out their assassination plan.