After their aristocrat father is unreasonably blamed for being a deceiver and murdered, Yoon Seo-hwa, her more youthful sibling Jung-yoon and their servant, Dam are sent to a gisaeng house (“gibang”). Declining to act as a gisaeng, Seo-hwa concurs in the wake of seeing the ruthless demolishing of her sibling. It is soon affirmed that her first “benefactor” will be none other than Jo Gwan-woong, the same man who sold out and executed her father. Before reaching him, Dam swaps garments with her so she can flee amidst the night, while Dam is attacked by Gwan-woong, who sends men to discover Seo-hwa.
Meanwhile, Gu Wol-ryung (an enchanted woodland defender and gumiho) notices an aggravation in the backwoods and discovers Seo-hwa who has passed out . He secures her from Gwan-woong’s men by uncovering his magical forces. When Seo-hwa gains consciousness, she falls in love with him too and weds him after knowing that both Dam and Jung-yoon were ready to flee and are protected. In reality, Jung-yoon had been hanged, while Dam had committed suicide. Wol-ryung, unable to let her know the truth, could not as well let her know that he was a gumiho.
Wol-ryung seeks Soo-jung ( a fortuneteller with various mysterious knowledge and skills) to help him to turn into a human so as to be with Seo-hwa. To become one, he must live 100 days without turning into his actual gumiho form, without taking a life (creature or human), and must not help anybody that needs support. In case that he falls flat, he’ll lose any possibility of regularly getting human, and as a punishment for not keeping the Gu Family Book conditions, he will turn into a devil for the following thousand years. Wol-ryung struggles to abide by these conditions, however one day, Gwan-woong’s men find Seo-hwa alone in the woodland. Wol-ryung races to help her, and uncovers his actual structure, slaughtering the warriors. Seo-hwa, alarmed by his hideous gumiho appearance, abandons him, and he is later executed by the noble trooper Dam Pyeong-joon, who had been told that the gumiho was killing innocents. Seo-hwa soon finds that she is pregnant with Wol-ryung’s kid and conceives a child. Understanding that the infant isn’t a creature like his father and sincerely mourning her disloyalty to Wol-ryung, Seo-hwa places her child in a bushel, and lets it float into the river not far from where minister Park Mu-sol was spending his morning with his family along the river’s side. She then defies Gwan-woong, yet is executed.
The baby is then found and embraced by the nobel Park Mu-sol.He grows up as Choi Kang-chi, apparently the child of Lord Park’s servant Choi. However, he is raised as a member of the Park crew. Despite the fact that Mu-sol’s wife Lady Yoon (Kim Hee-jung) never warmed up to him, Lord Park cherishes Kang-chi like his own child, and he is near the kins Tae-seo and Chung-jo, whom he adores despite the fact that she is promised to another man. Kang-chi is infamous in the town as a troublemaker, however he is great hearted and faithful, and adored by the servants at the Hundred Year Inn, which the Park family runs.
On the other hand, Jo Gwan-woong comes back to the town. He has some intelligence that the well off Lord Park has concealed fortune inside the Hundred Year Inn, and in his plan to assume control over the hotel, Lord Park is executed protecting Kang-chi. Gwan-woong tosses Tae-seo and his mother behind bars, and Chung-jo is sold to the gibang and persuaded by the head gisaeng, Chun Soo-ryun, to survive.
In the mean time, Gwan-woong gets charmed by Kang-chi and his apparently super-human quality. He utilizes mystery to place Tae-seo under a condemnation (hypnosis) that makes him accept that it was Kang-chi who killed his father and brought on the family disaster.
Dam Yeo-wool and Gon had been dispatched to the town by her father, now-martial arts skill master -Dam Pyeong-joon, to explore a series of homicides they think Gwan-woong is answerable for. Yeo-wool runs into Kang-chi: in light of the way she’s dressed and her expertise in martial arts and bows and arrows, he at first confuses her for a man. Yeo-wool witnesses the occasions that encounters the Park family, and intuitively helps Kang-chi when he is chased by Gwan-woong’s troopers. Throughout a battle, a trooper cuts off Kang-chi’s beaded arm ornament, which was utilized to hold his forces. Kang-chi converts into a half-human-half-monster and effortlessly vanquishes his foes. Sojung (the fortuneteller) later educates Kang-chi reality regarding his starting points, including the supernatural and tricky Gu Family Book, which holds the mystery to getting to be completely human.
Kang-chi is protected from a capital punishment and taken under the wing of Yi Sun-sin, a maritime leader. Yi Sun-sin, Master Dam, and the late Lord Park were a piece of a mystery aggregation securing the Joseon country against remote intrusion. Yi places Kang-chi in the combative technique school run by Master Dam, and there he is prepared physically and rationally and figures out how to control his conversions. Kang-chi and Yeo-wool fall head over heels in love. Be that as it may, a few hindrances stay in their direction: the proceeding villainy of Gwan-woong; the learning that it was Yeo-wool’s father who executed Kang-chi’s father; the return of Wol-ryung, who has transformed into a spirit sucking devil with no memories who must be murdered by his child; and Sojung’s ominous words that Yeo-wool is destined to die in the event that she stays by the side of the man she meets underneath the peach bloom tree under a crescent moon, which is none other than Kang-chi himself.