Season 1

A car explodes in the middle of the city and kills a person. The cause of the explosion is unknown. Cha Jae Hwan, a detective from the Violent Crimes Unit, notices something strange at the scene. Eugene Hathaway, an FBI agent on duty in Korea, helps him take another look. Later, Jae Hwan chases after a suspect, and in the end, he gets faced with a dark figure.

Jae Han gets greeted by Reporter Kim Hyo Kyung at the hospital, and Captain Han realizes that the incidents occurring now are related to the Chimera Case from 35 years ago. Jae Han tries to provoke elite surgeon Lee Joong Yeop with facts of Son Wan Ki's death, but Joong Yeop avoids anything that could incriminate him. While Jae Han suspects Joong Yeop, he gets pulled into another trap.

After Ju Seok's death, a special task force gets formed. Jae Hwan gets interrogated for being at the crime scene, and he tells them that the water caught on fire. However, no one believes him. Jae Hwan still suspects Joong Yeop as the culprit. With Eugene's help, he digs into the mystery and finds crucial evidence.

Without an attorney at his side, Joong Yeop agrees to get questioned by the police. Jae Hwan tries to get him to talk but ends up losing his pace. In Eugene's interrogation, he skillfully avoids answering any questions. Meanwhile, a call from Eugene's contact reveals his unexpected past.

Seoryun Medical Center's legal team stops the police's interrogation of Joong Yeop, the main suspect, and he is free to leave. After having drinks with the investigation team, Jae Hwan opens up and tells Eugene about his father's death. Now safely at his house, Joong Yeop recollects what happened at the Macheon Police Department when he was young. Later, Joong Yeop shows up at Eugene's lecture and brings up the past.

Jae Hwan and Eugene question the death of Lee Sang Woo that occurred 35 years ago. As they dig into the case file, they come across Bae Seung Kwan's name, the current chief of police at Joongsan. Slowly, the truth behind what happened 35 years ago becomes revealed through Seung Kwan and Hahm Yong Bok's conversation.

Jae Hwan tells Captain Ko Gwang Soo that Hahm Yon Bok was in charge of the Chimera Case 35 years ago and shares his suspicions surrounding Lee Sang Woo's death. While Jae Hwan and Eugene look into Joong Yeop and Lee Sang Woo's relationship, Joong Yeop tells an enlightening story. Meanwhile, another explosion takes place.

After the explosion, Hyo Kyung from UBS Newsroom visits Eugene at her office. She tells her that she believes the Chimera Case from 35 years ago is related to the current incidents. Since they don't have any hard evidence, she asks her to join hands and use the media to find the Chimera Killer.

Jae Hwan asks Chief Bae why Hahm Yong Bok got discharged 35 years ago, but Chief Bae becomes defensive and doesn't give him an answer. Meanwhile, Agent Hathaway finds suspicious things about Kang Sang Gu and keeps a close eye on him. However, Kang Sang Gu also has his eyes on her.

Kang Sang Gu is taken in as a strong suspect of the Chimera Murders. Right before when Seo Hyun Tae could have been in grave danger, solid evidence is found at Sang Gu’s home, and he confesses to all the murders he committed as the Chimera. Something however, tells Jae Hwan that the case is not over yet. His gut feeling keeps alerting him that the true Chimera might still be at large.

Joong Yeop tells Jae Hwan that his mom’s memories from before the accident are coming back. He has suspicions about the fact that the accident occurred 35 years ago. Later on, Jae Hwan gets a phone call on the day of his mom’s next appointment. He finds out that Joong Yeop quit his job at the hospital and left the country.

Joong Yeop claims that he assaulted people. He turns himself in at the police station, and a suspicious package is delivered to Chief Bae’s office. Meanwhile, the prosecution shows up and takes Joong Yeop to a remote mountain, even causing a car crash on purpose. They make him walk deeper into the woods at gunpoint until they arrive at a cliff.

While being taken by the questionable investigators from the prosecution, Joong Yeop takes control of the situation and flees the scene. The police start to chase him down, but Joong Yeop sneaks a secret message to Eugene. She goes to the place Joong Yeop indicates in his coded message with Jae Hwan. When they meet, Jae Hwan ends up pointing his gun at Joong Yeop.

Hyo Kyung calms Joong Yeop at Jae Hwan's house, and she learns about the whole truth behind the Chimera Case that happened in the past. Later, when Hyo Kyung meets Joong Yeop outside Jae Hwan's house, she notices a tail. She leads them right to Joong Yeop. As Jae Hwan rushes to help him, a bullet strikes Joong Yeop.

Jae Hwan finds out that the bullet found at Joong Yeop's crime scene was one that police officers were not issued to fire. Later, after watching an unsettling recorded video of his mother's interrogation, Jae Hwan rushes off to see his mother, who is now under supervision. Meanwhile, Kim Hyo Kyung appears on an internet show and reveals new facts about the Chimera Killer.

Joong Yeop recovers from his injuries and immediately wants to go stop Hyo Kyung. Jae Hwan goes to the broadcasting station to find Hyo Kyung, but he hears that she has already resigned from her position. Jae Hwan continues to track Hyo Kyung down, but when they finally come face-to-face, she already seems to have an ending in mind.