Damo, a police woman of the Choson Dynasty who is charged with a crime involving a woman, is a slave who belongs to the governmental office. With Chaeok’s wisdom, they find the suspect of the murder case, which took place at an annex of a good family. However, Captain Hwangbo Yoon rebukes Chaeok. Forgery, which is considered to be a dangerous threat to the social norm, takes place and the police officers discreetly investigate the crime. Chaeok dresses up as a man and goes to Kyeonggi Province to enforce undercover investigation. A large number of officers engage a nationwide undercover investigation. Despite her disguise, Sung-baek, a man who was leading a group of people, notices her gender and her martial arts ability and follows her secretly. Chaeok investigates a market place, knowing that there is a circulation of forgery. During the investigation, a woman and a man name Cheuk-ji Ma steal her bag. Sung-baek rescues Chaeok from danger and Whang-bo Yoon arrives late at the scene. Due to a misunderstanding, Whang-bo Yoon pulls out his sword against Sung-beak. Both of them realize each other’s skills by taking initiative action and they both become intensely nervous…
Chaeok clarifies the misunderstanding and they both put away their swords. After finding out that Chaeok is a police woman, Sung-baek leaves. Yoon assumes that he is a student of a legendary swordsman, Hyun-ki Whang. Yoon and Chaeok’s crew head back to the station. Due to the foot injury, Chaeok falls behind. She stops to dip her feet into the water and reminisces about her mother. In her childhood, her name was Jae-hee Jang. Under the parental roof of Lord Il-soon Jang, she lived happily until the age of seven with her fourteen year old brother. Her family was torn apart when her father was accused as a traitor. She did not know of her mother’s fate and departed with her brother Jae-moo. When she arrives at the station, she finds Yoon waiting for her. He tells her to grab the wooden sword and strikes her wrist to make her drop it. ‘What am I to you?” asks Yoon bitterly, and he behaves angrily towards her speechlessness.
Yoon recalls the younger days when he first met Chaeok.
Lord Whang was extraordinarily intelligent and talented. Having high expectations for Yoon, a child born by a concubine, he becomes disappointed and sends him off with a slave name Jae-hee into the deep mountains, telling him to train. He trains under the Great monk name Su-wol, the former leader of the monk soldiers, and Jae-hee, who followed them like a shadow, also becomes tactful in the art of swordsmanship. Monk Suwol recommends Yoon to the police captin Sae-uk Cho. He immediately senses his swordsmanship and good nature and hires him. Yoon tells Lord Whang that he wants to bring Jae-hee as a damo. Lord Whang reads his mind, and tells him not to take advantage of her.
Yoon and chaeok’s team visit a funeral of another officer who was killed while investigating a case of forgery. They discover evidence from the officer’s clothes and shoes. Byung-tak, who is devoted to helping Chaeok, gives her mountain ginseng which was given to his father, administrator Ahn, as a bribe. Chaeok and Detective Ju-wan Beak disguise themselves as ginseng collectors. Many people gather to the pub to see the valuable mountain ginseng, and Sung-baek, disguised as a blind man, also joins the crowd. He pretends to be a ginseng expert and steals the ginseng after directing their attention elsewhere.
Chaeok chases him after she finds out, but only after he gave the ginseng away to a poor man and her mother. The poor man returns the ginseng, and she sells it to him at an extremely low price without any regrets.
Sung-baek back informs Dal-pyeong Choi, who is trading forged money with a product. Dal-pyeong tells him that merchants are perceived as victims and that he has already eliminated an information source. He also tells Sung-baek to watch out.
Chaeok proudly shows the forged money she collected and the criminals she arrested while making her report. Yoon becomes furious towards Chaeok, saying that she dangerously risked her life. Chaeok returns her ID and badge, saying that she has caused too much trouble.
Yoon is bewildered by her act but soon regains control, and orders the other officers to arrest the motel owner and the crew who are the main suspects of forgery and its circulation. Won-hae arrests them at the ferry mooring, but they testify that they didn’t know the nature of their use of the money. Unfortunately, the investigation returns to its starting point.
Chaeok starts to drink in the early afternoon at a pub and sees men harassing a mother and her daughter. She becomes furious, but then she ignores them knowing that she no longer belongs to the police. Yoon-hae and Yoon witness the scene over the fence and throws her the badge and her Id. She regains her responsibility as a damo and arrests them.
Chuk-ji Ma and Gak-chul break out of their cells and run into Chaeok who is waiting for them. Sung-baek, who was on the lookout to rescue them, sees Yoon and his military officers arrest the escaping men. When Yoon gives an order to fire, Sung-baek rescues them in a rain of gunfire and sees Chaeok again.
When Sung-baek returns to the mountain, he experiences an uncomfortable conflict with Dal-pyeong, and Gak-chul prepares revenge. Chuk-ji Ma and Chaeok succeed in infiltration. However, they fall into Dal-pyeong’s trap again. Sung-baek, who has met Chaeok in the past, frees them with mercy. They King himself censures the break-out of the prisoners and Sae-ok Cho reports that it was a set-up. They receive fifteen extra days to resolve the problem. However, Yoon is dismissed. Chaeok, who fails to join Sung-baek’s crew, waits for another chance by the ferry moorings. Sung-baek and Gak-chul becomes nervous when they see police doing a check to find the escaped prisoners. Right then, Chuk-ji Ma brings confusion in a middle of the crowd and Chaeok comes out of the water to rescue Sung-baek and Gak-chul. Afterwards, she hides back under water and dives to the point where Chuk-ji Ma waits. Sung-baek, who saves his life by getting on the boat, decides to join Chaeok’s crew.
Won-hae and a lady wait to hear from Chaeok’s crew. They run a pub near a mountain and try to communicate by using a messenger pigeon. However, they become anxious due to their lack of progress. Chaeok secretly comes down from the mountain and reports that there are too many military soldiers. She explains the difficulty of finding a forgery house and hands them a map of the mountain. At the police station, Chi-oh Cho becomes the next Captain of the squad. Chaeok finds the forgery house, but she can’t find the main tool which is used in the actual making. She goes to a village where leprosy patients live, and takes care of them to earn Sung-baek’s trust. She recognizes Hak-cheol’s face, who Sung-baek calls an uncle.
Chaeok then recalls the images of her past. Sung-baek also feels strange and asks of her past, but their answers don’t seem to match…
The military soldiers fire endless rounds from a matchlock gun, and Sung-baek quickly rescues Chaeok from the trouble. Suffering a critical injury, Chaeok faints. At the same time, Yoon dreams of Chaeok, which gives him bad feelings. He recovers from his illness with the sincerely nursing care of Nan-hee. Sung-baek treats Chaeok’s back by cutting the skin. In a sympathetic tone of voice, he asks of the origin of her strength that makes her withstand the pain. Chaeok puts her head down in silence. Feeling worrisome, Yoon goes to the police station to meet detective Baek, but he is treated coldly by the Captain and returns dejectedly. Won-hae sends an urgent message about Chaeok’s critical condition. In desperation, Yoon goes to Captain Sae-uk Cho and requests suppression. However, he tells him that there isn’t enough evidence and he should wait. Ju-won tells him that he’ll take care of everything and pushes him to go. Chaeok battles Sung-baek’s secret messenger Su-myeong in attempt to arrest her. Due to her injury, she becomes weakened, but Yoon shows up to save her.
Sung-baek, who welcomes Chaeok as if he waited alone by the mountain, tries to tell her that he’s not a part of a gang. He tells her that he will create a new world with people who share the same desires. He invites her to join them but she shakes her head. Cheaok, Ju-wan and Won-hae save Chuk-ji Ma from a fire and follow Chi-oh Cho down to the valley. All of the military were murdered before Chi-oh’s arrival, and Chi-oh also loses his life over a battle against Sung-baek.
Chaeok and her crew become completely powerless. The funerals of over 150 soldiers who lost their lives and Chi-oh are held in collaboration. Captain Park cries out that he is a foolish leader and faints. Chaeok tries to explain that it was her fault by meeting the law officer, but he throws her down. She hears the heartbreaking words of Yoon in prison: ‘Stop trying to save me and forget about me’. Running out of options, she tries to break into the palace to meet King Sookjong, and she almost loses her life at the hands of the King’s security guards.
Chaeok writes her last words to Yoon and attempts to break in to the palace. She tries to meet King Saejong, but her life becomes threatened by King’s security guards. However, seeing the wholehearted effort and sincerity of Chaeok, the King reads her mind to find out that there’s a spy in the palace. The king secretly releases Yoon and Captain Cho for an investigation. Chaeok suffers from a critical condition and Yoon forces the doctor to cure her. The doctor tells him that there is no way to cure her. Yoon can’t stop the tears rolling from his eyes and brings her to the temple which they spent their childhood. He and his master monk Suwol use chi treatment to try and save her life. They try every possible method to bring her back, but she doesn’t regain consciousness. He reads about their despairing moments and the letter she wrote before she left to break into the palace. He cries out loud, saying that she is the reason why he lived. Yoon decides to engage mercy killing and starts the ceremony.
Captain Cho, who becomes furious with Yoon’s illegal activity, forgives him because of Nan-hee’s sincere request. He demands Yoon to send Chaeok to a different area and get married to Nan-hee if he wishes to stay at the station.
Chaeok cries with all her heart when she finds a temple with her parents’ gravestones. Sung-baek visits the village to console the lost souls and hears of a visit made by a young woman. He suspects that it is his lost sister Jae-hee, and feels sorry that he missed her. The police discover that the forgery gang is infiltrating the government offices. They become surprised that their primary objective is not forgery of money but treason. When Chaeok returns healthy, Yoon no longer hides his love towards her. Chaeok stubbornly tells him that she has to arrest Sung-baek. Yoon tells her that even if she finds him, she can’t defeat him, and he also tells her that he’ll get married to Nan-hee. Chaeok becomes a soldier and Byeong-taek becomes relieved by the great news.
Chaeok and Chuk-ji Ma disguise as gangsters and wait for Sung-baek’s crew. After hearing the news, Sung-baek faces Chaeok’s military group. Yoon arrives to have a personal battle with him. Gak-chul saves Sung-baek from danger by sacrificing his own life. Chaeok chases Sung-baek alone and suddenly they fall together into a deep hole in the ground. They pull out their swords against each other, but they don’t take any actions. They smell death in the air and support each other in hopelessness. Taking the risk that it might close the hole, they fire an emergency signal.
Won-hae looks at Yoon, who is focusing on the search of Sung-baek and Chaeok, and tells him not to lose his men over personal reasons. Yoon manages to control his anger and tells him that this isn’t personal. A high ranking law officer comes to Gamyang and orders Yoon to return to Dosung. Yoon sends Won-hae back to Dosung, but he tells him that he’ll stay behind to support their investigation. Chaeok panics when Sung-baek’s condition becomes worse. However, she nurses him with all her heart to bring him back to life. Sung-baek wakes up to find Chaeok asleep, and feels her warm heart. Soon, they both take out the anger they had. Yoon and Captain Baek discover that Officer Yang is a part of the treason. They wait for Won-hae to return and keep their eyes on Yang’s movements. Yang tries to run when situations become worse, but Yoon stops him by blocking off the road. Cheaok gets bitten by a poisonous centipede, and without recognizing that his body is also being poisoned, he saves her life. When Chaeok regains consciousness, she sees Sung-baek dying. She cries in despair. At last, she finds the exit…