Lee Da-Il is a private investigator. He was formerly in the military, but a whistleblower case led to his discharge. Jung Yeo-Wool becomes his assistant. She is a fearless woman. They work together to solve a mystery surrounding the death of a younger sibling. They also work together to solve other cases, some involving ghosts.

Da Il suspects that the teacher at the academy is the person who abducted the three kids. While working on the case at the office, an aspiring detective pays him a visit. However, after a strange turn of events, Da Il meets a tragic end.

Yeo Wool thinks it's strange that Da Il disappeared from the crime scene, leav-ing the kids behind. The police investigating the case also finds the case strange. Meanwhile, Yeo Wool keeps looking for Da Il and worries that some-thing might have happened to him.

Da Il comes to Yeo Wool's house and asks her about what she knows. From Yeo Wool's story, he learns more about the mysterious woman he saw. Togeth-er, they start looking for clues.

The manager of the restaurant Yi Rang used to work at jumps off a building af-ter saying something ominous. Da Il can't help but feel sympathy toward Yeo Woo because he knows very well how she must be feeling right now. The woman in red is coming for them.

Da Il gets a feeling that Yi Rang's hearing aid will provide a clue to find out more about the woman in red. With Yeo Wool, he follows the lead. The woman in red's next target is the principal of the pre-school.

In order to pursue the woman in red, Da Il realizes that he'll need help from Sang Seob. Yeo Wool takes Sang Seob to the location where Da Il was buried, but Sang Seob doesn't believe anything she says.

When Sang Seob finds Da Il's identification tag, he accepts the fact that Da Il is dead. Da Il and Sang Seob work together to find leads with the help of Yeo Wool. Meanwhile, the woman in red gives Da Il a warning.

The woman in red warns Da Il about how she'll kill everyone that loves him. Sang Seob becomes the next target. While working on the case, Sang Seob gets attacked. Da Il tries to find a way to help Sang Seob.

It turns out that the police officer Sang Seob was looking for killed himself 20 years ago. Da Il senses that Sang Seob is in imminent danger. They must find him before it's too late.

The “A Few Good Men” Team rushes to the hospital where Sunwoo Hye is supposedly hospitalized. However, they quickly discover that Sunwoo Hye had already made a run for it. Through the help of Sunwoo Hye’s nurse, Jeon Deok Joong, Da Il and Yeo Wool chase after Sunwoo Hye from all possible directions.

Yeo Wool and Da Il go and meet a shaman hoping to gain information on how to kill a fetch. Knowing that they would get into trouble, Chae Won goes to help them and ends up saving them in the nick of time. Later, the group decides whether or not what the shaman had told them is worth doing.

Da Il learns how to touch objects and stabs Hye with a knife before Yeo Wool does. Hye becomes a living person and runs away from the hospital after killing four medical staff, and Yeo Wool thinks it all happened because of her as she was not the one who stabbed Hye.

Jeong Dae asks Yeo Wool to tell the truth as her fingerprint was found at the crime scene. Yeo Wool tries to tell Jeong Dae that she was the one who stabbed Hye, but Da Il tells her to deny it. Meanwhile, Da Il records a video of a man who saw Hye at the hospital and sends it to Eun Chong.

Sunwoo Hye is trying to kill hundreds of lives by controlling Gyeol. The team must find out why and how she is intending on killing those people. Da Il re-members something about Sunwoo Hye and tries to connect the dots.

Just when Gyeol is about to stab himself, Da Il disappears. Sunwoo Hye goes to Deok Joong and asks him what really happened to Da Il. Not knowing if Da Il will appear again, Yeo Wool waits for him.

Sunwoo Hye relentlessly harasses Yeo Wool. She tries to control Gyeol's feel-ing of guilt in order to get rid of her. Meanwhile, the team tries to find out where Da Il's body is being kept.

The team arrives at the house they located, but Da Il is nowhere to be found and they only find traces of him. Sun woo Hye confronts Yeo Wool and gives her an opportunity to take revenge. Sang Seob comes to help and falls into a trap.

A reporter who seems to know something about Da Il pays the team a visit. Sunwoo Hye is tracking down her own mother by using Gyeol. Yeo Wool and Da Il are always a step behind Sunwoo Hye, but they find a lead at the pharmacy.

Jeong Dae arrives in time to save Yeo Wool. Yeo Wool is worried that Da Il might turn into an evil spirit forever. Upon meeting her mother, Sunwoo Hye asks her why she never came back.

The reporter publishes an article about Da Il which gets everyone interested. Da Il goes to Jeong Dae to ask for a favor. The team finds the missing link that will help them find Da Il's body.

After talking with Sunwoo Hye, Da Il's anger grows even bigger. The men who are being controlled by Sunwoo Hye try to take the hearing aid from Yeo Wool. Da Il goes after the source of his anger.

Along with finding Da Il's body, Sunwoo Hye also wants to possess Yeo Wool. Da Il must find a way to get rid of her without harming Yeo Wool. Meanwhile, Jeong Dae is looking for Da Il's body on his own.

Da Il arrives at the grape farm and finds his body. Yeo Wool manages to find where Da Il went and goes after him, but Sunwoo Hye is already there. Chae Won confronts Sunwoo Hye and tries to buy some time for Jeong Dae.

Sunwoo Hye's goal is to kill everyone around Yeo Wool and Da Il. Jeong Dae tells Yeo Wool that it'll be better if he doesn't know anything about her plans. Meanwhile, Gyeol takes Sunwoo Hye to Da Il's body.

After harming Gyeol, Sunwoo Hye attempts to flee. Da Il leaves Gyeol to Yeo Wool and goes after Sunwoo Hye. The team finally finds Da Il's body, but it's in a very bad condition.

Sunwoo Hye takes Attorney Baek hostage and escapes from where she was being confined. The people who have suffered because of Sunwoo Hye all gather forces to track her down. Meanwhile, Sunwoo Hye executes her plan to kill everyone that Da Il loves.

In order to stop people from getting hurt more, Yeo Wool decides to let Sunwoo Hye possess her body. Da Il asks her not to, but Yeo Wool is not willing to change her mind. Chae Won and Da Il must come up with a new plan to get rid of Sunwoo Hye.

Yeo Wool is back home. After getting some rest, she heads to the hospital where Da Il is being treated. However, Da Il thinks it's not over yet.

In order to protect the people he loves, Da Il chooses to sacrifice himself. Yeo Wool remembers him as the person who tried to understand Sunwoo Hye until the last moment. When she goes to bed one night, Yi Rang comes to her.

After Da Il's death, people go back to their lives and Yeo Wool returns after a long journey. Upon her arrival, Yeo Wool witnesses something strange yet familiar. Sunwoo Hye is gone, but there are still threats out there.