As a widow, Yeo Hwa cannot leave her home and has to mourn her late husband day and night. However, she often sneaks out at night and helps people in trouble by disguising herself as a man behind a black mask. One day, she hears that Kkot Nim, the little servant she adores, was taken for her father's debts. She goes to the inn where Kkot Nim is and sees Officer Park trying to take her by force.

Yeo Hwa decides to save Kknot Nim by herself. The moment she walks into Pil Inn with her face covered up, she spots Kkot Nim taken away by Soo Ho, the officer of the Capital Defense. Meanwhile, the Minister of Finance summons Soo Ho as a masked man sneaks into his house and steals his precious painting.

Soo Ho realizes Kang Pil Jik of Pil Merchant Guild is also searching for the painting that Yeo Hwa stole from the Minister of Finance. Soo Ho leaves a note to the masked hero at Myungdo Inn to give a warning. Meanwhile, Yeo Hwa attends a relief with her mother-in-law and high officials' wives, and a child goes missing out of the blue.

Yeo Hwa and Soo Ho find where Pil Jik has been hiding kidnapped children in Pil Inn. They manage to rescue them but are at odds again about where to take the children. Soo Ho wants to take them to the Capital Defense as witnesses to Pil Jik's crime, but Yeo Hwa wants to send them to a safe place first. Meanwhile, the Minister of Finance passes away, and his servant gets arrested as a suspect of murder.

Aware of Yeo Hwa's true identity, Soo Ho takes measures to prevent her from engaging in any reckless behavior. Yoon Hak and Lee So discover that Sung Hoo is the King's Guard who vanished after receiving a secret order from the previous king fifteen years ago. Meanwhile, in her quest for any signs of her brother, Yeo Hwa encounters an unexpected approach from someone.

The King and Yoon Hak find it strange that Ji Sung took in Yeo Hwa, the sister of Cho Sung Hoo, as his daughter-in-law. They believe that he took her as hostage to catch him. At the same time, Ji Sung invites Yoon Hak and Soo Ho to his house. Meanwhile, Nan Kyung wants to talk to Yeo Hwa about her family in private.

So Woon looks into Nan Kyung's background and relays the information to Soo Ho. Yeo Hwa also gets a tip from Nan Kyung that her brother's disappearance is related to the matter at the palace. Yeo Hwa asks Ji Sung about her brother, but he tries to hide the truth from her. When Ji Sung secretly leaves the house in the middle of the night, Yeo Hwa follows him.

From Yoon Hak and Su Ho, Yeo Hwa discovers that Ji Sung had her marry into his family to have leverage over her brother, Sung Hoo. Also, Su Ho tells him about his true identity and his parents. They believe Sung Hoo is the one who has the evidence of Ji Sung's treason. Meanwhile, Geum Ok leaves the house to pray for her son in the temple, and Jeong returns home.

Pil Jik fails his mission to take Nan Kyung's life and tries to flee. Ji Sung decides to remove Yeo Hwa before she finds out more about his plot. Also, he threatens the King with the Queen Dowager's safety. Meanwhile, Soo Ho discovers that Ji Sung's son came back alive.

Ji Sung finds out Soo Ho is the son of the former Head of the King's Guard, and Jeong requests Soo Ho to have a chat with him in private. Meanwhile, the King invites Ji Sung and his family to the palace to celebrate Jeong's return, and a surprise guest awaits them.

Yeo Hwa cannot believe the fact that Sung Hoo already died at the hands of her father-in-law, Ji Sung. Pil Jik also confesses that Ji Sung ordered him to murder Sung Hoo and Im Kang's family. However, even though his sin has been revealed to his family, he does not bat an eye and tries to threaten the King. Yeo Hwa loses her mind and decides to kill him right away.