Nok Du, who is living on a small island, witnesses his father and brother get attacked by a group of assassins. He decides to leave home and find out who they are and work for. He follows the leads and arrives in Hanyang.

Nok Du disguises as a woman and enters the village where only widows are allowed to live. When Nok Du finally finds the female assassin that he has been looking for, a group of widows takes him somewhere.

At night, Nok Du happens to overhear the conversation of a group of widows who look like trained assassins. Nok Du starts to follow one of them into the woods.

Nok Du and Dong Joo become close. Nok Du helps out Dong Joo when she is having a hard time because of her injured hands. Dong Joo says that she wants to treat Nok Du like an older sister.

Nok Du persuades Dong Ju to let him stay in the village. The widows talk about a man who sneaked into the village last night, and they plan to catch him by making a composite sketch of him. Nok Du decides to give the widows misleading information about the man to confuse them.

Dong Ju hears a rumor about the man who broke into the village the other day. She realizes that it is not a good idea to let Nok Du stay in the village. She asks Nok Du to leave the village.

Nok Du decides to help Dong Joo so she doesn't have to be a gisaeng. Nok Du gives up the mission that the widows of Muweol Corps gave him. He goes to meet Lady Chun with an idea that can help Dong Joo. Meanwhile, the widows of Muweol Corps agree to give Nok Du the second chance.

Dong Joo keeps being reminded of her childhood and family after she came to Hanyang. She visits the house she used to live when she was a child. That's when she runs into Yul Mu. Meanwhile, Nok Du hears that the real Lady Kim and her servant got caught.

Nok Du returns to the village for widows with Dong Joo and Yul Mu after completing his mission in Hanyang. However, the widows and gisaengs in the village think that Nok Du likes Yul Mu. Meanwhile, Yun Jeo and Hwang Tae see that a group of assassins are in front of their place.

Nok Du is curious about who Dong Joo likes. He asks her who it is, but she never tells him. Nok Du decides to tell Dong Joo his feelings for her, but Dong Joo tries to keep her distance from Nok Du.

Yul Mu finds out that Nok Du has been pretending to be a woman all this time and that Dong Joo has been looking out for Nok Du. Yul Mu wants to know if Dong Joo has feelings for Nok Du. And Nok Du tells Dong Joo that he will make her fall in love with him.

After the widows of Muweol Corps left for Hanyang, Nok Du and Lady Chun find out that the widows are in a trap. Lady Chun asks Nok Du to go help out the widows, and that's how Nok Du becomes a member of Muweol Corps.

Heo Yun and his fellows think that the King might have noticed about their plan, so Heo Yun orders the widows of Muweol Corps to move their base. Meanwhile, Nok Du happens to overhear the conversation between Dong Joo and Yul Mu.

Nok Du meets Hwang Tae at Yul Mu's house. Nok Du insists that he and Hwang Tae should hurry and leave the place, but Hwang Tae refuses. Instead, Hwang Tae tells Nok Du a big secret about his birth.

Because of the attack by robbers, the village for widows is destroyed and many widows get injured or killed. Nok Du risks his life and helps the widows without disguising himself. Nok Du is also seriously injured and faints. When he wakes up, he realizes that Dong Joo has left without saying goodbye.

In Hanyang, Dong Joo is trying to get a job in the palace by bribing court ladies. Nok Du visits Heo Yun again. Heo Yun takes Nok Du to the room where Yun Jeo is staying.

The widows of the Muweol Corps are confused and want to find out who is behind the attack of the village, Yul Mu tells them that it was Heo Yun's order. He also suggests that the widows help him to create a new world. Meanwhile, Nok Do tells Dong Joo that he will never let her leave him again until she pays back what she owes him.

When Nok Du and Dong Joo are walking on the streets, an old lady stares at Dong Joo as if she knows Dong Joo. And Nok Du and Dong Joo run into the King again. The three of them go hiking to relieve the King's insomnia. Yul Mu walks into a trap set by Nok Du.

Nok Du finally meets the King at the palace and is assigned to assist a senior chief administrative officer. Meanwhile, Heo Yun visits the King to warn that Yul Mu should not be trusted and is plotting treason.

Heo Yun continues trying to convince that Yul Mu is plotting treason, the King still doesn't believe him. Nok Du runs into the Queen in the palace and notices that she is wearing the same jewel as the one he possesses.

The King pays his visit to Heo Yun who is imprisoned in the dungeon. Meanwhile, Dong Joo finally gets a job at the palace. Nok Du visits her workplace and helps her work.

Yul Mu finally finds Dong Joo in the palace. Meanwhile, Yun Jeo and the Queen secretly meet in a private house. Yun Jeo tells that the Queen's son is still alive and that she should protect him from the King.

Jung Yun Jeo is taken to the prison, and Dong Joo is shocked that the Chief Administrative Officer is the King. The King begins to torture Yun Jeo.

Nok Du plans with Ssook to steal the Merit List from Grand Prince Neungyang. Nok Du goes to see the King with the Merit List. When Nok Du sees the King and Yun Jeo in prison, he happens to hear what's truly on the King's mind.

Dong Joo finds out the true identity of Nok Du. Meanwhile, Nok Du is promoted as the Royal Guard and is ordered to stay by the King at all times.

Nok Du spreads the rumors around the town about the King and himself. Dong Joo also plans to not hide. Therefore she decides to end her relationship with Nok Du.

Dong Joo escapes from the palace and moves alone to kill the King. Meanwhile, Nok Du escorts the King to his way to the shrines.

The revolting army takes away the castle. Everyone seems to be after the King, but the King himself just realizes that his trusted royal guard is Nok Du.

Dong Joo and Nok Du share their honest feelings toward each other. They promise to be together despite their complicated family history. Nok Du takes off to fight against the revolt led by Grand Prince Neungyang.

Dong Joo can't sit still and wait for Nok Du. She gathers her things and sets off to the palace. She enters the palace to see Neungyang aiming at Nok Du and throws herself in front of his arrow.

Nok Du and Dong Joo manage to get out of the palace thanks to the Queen's help. Yul Mu and his men go after Nok Du and Dong Joo. However, Nok Du and Dong Joo end up being surrounded by Yul Mu's armed forces.

Nok Du volunteers to keep working with the widows. And the wedding ceremony for Nok Du and Dong Joo is held. Every resident on the island comes to celebrate the couple.