Season 1

During an interview for the Police University, Chae Do-Jin nonchalantly confesses that he is the biological son and the witness against the infamous serial killer, Yoon Hee-Jae. Since Hee-Jae’s crime was serious, everyone knew about him and what he did. Words spread quickly across the interviewees, and some start looking at him in fear.

Nak Won and her family move from Seoul to the countryside after her mother and actress, Jee Hye Won, decides to take some time to rest. On her first day of school, she is reprimanded by a teacher for not wearing neat clothes. Suddenly, Na Moo comes to her rescue and stands up for her. Meanwhile, a murder of an elderly couple has occurred.

Nak Won finds Lucky's name tag in front of Hui Jae's house, but Hui Jae shows up. Na Moo finds a dog locked up in a cage which was Lucky. Hui Jae explains why Lucky happened to be here, but Nak Won and Na Moo finds it suspicious.

Na Moo protects Nak Won from friends who try to harm her. Ok Hee hears Hui Jae is having an affair with various women and she tries to deny it. Hui Jae approaches a lady at the bus stop and asks her to take his ride.

Ok Hee takes So Jin and runs away from Na Moo's father. Na Moo tells Nak Won about his feelings, but he sheds tears at the same time while telling her so. Meanwhile, in the present, Do Jin is haunted by the memory of his father.

Lack of acknowledgement and mistreatment from a colleague aren't enough to bring down the passionate actress Jae Yi. However, she is reminded of the past when she finds out about the release of Hui Jan's autobiography.

Ji Ho is following Jae Yi to get the scoop on her past, and other reporters start to dig in to get an exclusive story for the tabloids as well. They put Jae Yi in a tight corner, and Do Jin rescues her from them. She realizes right away that it is none other than Na Moo himself, but she passes out in his arms.

Pyo Taek, Jae Yi's manager, gets furious with Reporter Park as she revealed Jae Yi's past to the media. The victims' families boycott Hui Jan's autobiography. Do Jin's family receives anonymous threatening calls after the book went viral, thus they call Do Jin to tell him not to have any visitors until his graduation.

Hui Jae is caught by the police because of his own son, Na Moo. He tells Na Moo that wickedness is not something that can be developed but that it is in one's blood. Meanwhile, Hui Jae's autobiography puts the spotlight on Jae Yi and her family. Do Jin decides to be interviewed and even asks for his face to be revealed.

During the Police Academy's graduation, Do Jin is awarded the Presidential Award. Suddenly, a group of Hui Jae's victims' families barge in and throw eggs at him. They tell him that he is no different from his father and that he does not deserve to be a police officer. Amongst this chaos, Hee Young smiles while she takes photos.

Jae Yi joins the Korea Arts Award. Meanwhile, Do Jin becomes a detective of violent crimes. As he is out on a stakeout to catch the culprit of the recent assaults, he gets injured and goes to the hospital.

Jai Yi faints after opening a gift that was delivered to her waiting room at the awards. Do Jin and Jae Yi happen to be taken to the same hospital, and they end up meeting at the lobby. Later, Jae Yi visits Do Jin at the police station.

Do Jin finds out that a bloody hammer was delivered to Jae Yi as well as a card written to Jae Yi's real name, Nak Won. He asks Senior Inspector Ko to hand over this case to him, stating that these are signals targeted to the case 12 years ago. Despite the senior Inspector's plea not to get involved, Do Jin takes on the case.

During Jae Yi's shooting, the lights suddenly turn off. As soon as the lights turn back on, Do Jin finds Jae Yi trembling with fear. The shooting gets called off, and Do Jin shows her a photo of his own brother, Hyun Moo, and asks if she has seen him. He tells her that if she ever encounters him that she should run away because he is considered dangerous.

Hyun Moo is suspected of being involved in the incident at the filming site. To protect Jae Yi from him, Do Jin goes after his brother with an arrest warrant. Jae Yi is saved by Do Jin once again, and she falls asleep in Do Jin's arms dreaming of Na Moo keeping her side.

Moo Won makes a phone call to Hee Young and threatens her not to bother Nak Won anymore. However, she threatens him back saying that she can sell his story with Nak Won to a tabloid. Hyun Moo causes a disturbance at Ok Hee's restaurant and runs to Jae Yi's place with a weapon in his hand. There, he meets his brother who was waiting for him.

Hyun Moo breaks into Jae Yi's garage, but Do Jin tries to stop him from killing her. However, he falls into a serious condition after his brother stabbed him. Covered in blood, Jae Yi brings him into the hospital. With Ok Hee keeping her side, Jae Yi prays for Do Jin's recovery while her lover is undergoing a surgery.

Hyun Moo comes across his half-sister So Jin and tells her that he attacked Do Jin to prove himself to their father. So Jin tries to stop him from committing further crimes but he gets away. Ok Hee pays a visit to Hui Jae for the first time in 12 years to warn him not to bother their children anymore, but leave them alone in peace. However, Hui Jae reminds her that they are not only suffering from his sin but hers as well.

Hyun Moo finally faces the real culprit who orchestrated the residential area murders and the attempted attack on Jae Yi on behalf of Hui Jae. Meanwhile, Hui Jae is confined to a punishment quarter for brutally assaulting his correctional officer. Hee Young pays a visit to him in prison to stir him up again.

Do Jin recovers from the wound faster, thanks to his family and Jae Yi. After Do Jin got discharged from the hospital, Jae Yi asks him out on a date. The young couple goes on a picnic and has a great time together not worrying about the problems around them for a moment. A reporter from another magazine comes to visit Ok Hee to give her a hassle, but Moo Won helps her to get rid of the annoying reporter.

Unable to keep his feelings hidden any longer, Do Jin confesses his love to Jae Yi, and she replies back with a kiss. They both tell each other that it's crazy that they like each other but that they cannot help it. Meanwhile, everyone from Gowon Station who were on the case 12 years ago are summoned for an interrogation in secret.

During an interrogation, Hui Jae threatens Moo Won and tells him that Nak Won will be the next victim. Enraged, Moo Won grabs him by the collar and warns him not to touch her. Meanwhile, news spreads regarding Reporter Park Hee Young's death. Do Jin goes to the crime scene and finds a bloodied hammer.

Filled with anger and hatred against his son, Hui Jae plans for something that he has been waiting for many years. Now, Do Jin finally starts to investigate Yeom Ji Hong, the copy cat of Hui Jae, and Jae Yi cannot help herself but worries about her lover's safety. The young couple needs each other now more than ever.

Do Jin visits the broadcasting station to meet Jae Yi and catches her shooting a romance drama with a handsome actor and gets jealous of him. The copycat of Hui Jae, Yeom Ji Hong, shows up in front of So Jin, but fails to assault her because of Hyun Moo. Meanwhile, Hui Jae gets in a car crash while in transport to another facility.

Hui Jae manages to escape from prison, Worried about Jae Yi, Do Jin goes to her house and comforts her. He promises her that he will put everything back to normal and suggests they stay together for the time being. Meanwhile, the police suspects that Hui Jae is in Seoul.

Moo Won hands over the video footage he received from Hyun Moo to Do Jin. Do Jin focuses on finding the copycat killer, Ji Hong, and Ji Hong keeps asking for permission to kill Do Jin. Meanwhile, Hui Jae tracks down Ok Hee.

Hyun Moo visits Ok Hee's restaurant but only finds it closed so he goes home to check on her. Outraged by what Hui Jae has done, Do Jin goes straight to Ji Hong and makes him give the name of Hui Jae's helper who has been working with him all along. It is a woman in her 40's and Do Jin starts digging into who she is and her whereabouts.

Do Jin finds Hyun Moo and Ok Hee lying on the floor when he gets back home. Moo Won and Do Jin finally confirm the identity of Hui Jai's helper, Jeon Yoo Ra, and start looking for her. Meanwhile, Hui Jae visits the bamboo trees to retrieve the hammer he hid 12 years ago.

With Hui Jae on the loose, Nak Won and Na Moo worry that the life they built up until now might get ruined. Na Moo visits Hyun Moo at the hospital to thank him. Both Nak Won and Na Moo are trying desperately to become happy again.

Na Moo gets a call from Yoo Ra that she wants to turn herself in. While Na Moo is distracted, Hui Jae gets what he wants. Na Moo must find a way to protect what's most valuable to him.

To rescue Jae Yi from Hui Jae, Do Jin puts himself in harm's way. Hui Jae finally confronts Do Jin in person and keeps provoking his son to kill him. Hui Jae demands Do Jin tha e should succeed to his father and proves how evil prevails.

Everything is back to normal after Do Jin caught Hui Jae and put him in custody. Moo Won finally approved Do Jin dating his sister, and Do Jin gets promoted to Senior Inspector for what he has done. Hui Jae and his accomplices are charged with multiple counts. After many years of suffering, Jae Yi and Do Jin finally find peace and salvation.