Psychopath Diary

Dong Sik, a stock analyst at Daehan Securities, takes the blame for a report he didn’t write that caused a leading pharmaceutical company’s stock price to fall. He decides to end his life and attempts to jump. However, a murder about to happen catches his eye.

After the restroom incident with Mr. Gong, Dong Sik becomes jubilant. His world of being a pushover ends, and he begins to believe that he is indeed a predator. Meanwhile, Seo In Woo, the serial killer, starts to look for his missing diary, and Shim Bo Kyung, a patrol officer, discovers something strange in the violent crimes and attempts to find the homeless man who vanished.

Dong Sik determines to kill Seo Ji Hoon and secretly plans how he's going to do it. In Woo tells Dong Sik about a company going public and urges him to buy as many shares as he can. Meanwhile, Ji Hoon and Chan Suk resort to the old-fashioned way to get rid of Dong Sik, and Bo Kyung goes on a suspicious call.

In Woo tries to get close with Dong Sik after secretly following him and seeing him kidnap Ji Hoon. In Woo becomes the director of the Asset Management Team and promotes Dong Sik to assistant manager. Dong Sik later finds out that he had written a suicide note on the day of killing the homeless man and is thrown into confusion. Meanwhile, Bo Kyung, who is after the serial killer, starts to find Dong Sik's behavior strangely suspicious.

Bo Kyung and In Woo both chase after Dong Sik for different reasons. And soon, both get closer to what they are after. Bo Kyung gets an unexpected hint from Dong Sik about the serial murders and starts to investigate a missing person case. Meanwhile, In Woo starts to become more active.

Dong Sik wants to stop Bo Kyung from looking into the murder case happened at Goseong Chemical, so he follows her and offers help. Dong Sik gets to know Nergui by chance when he sneaks into Goseong Chemical. Nergui asks for Dong Sik’s help and tells him that Jin Goo doesn’t kill himself. Meanwhile, an open investigation begins after a dead body is found in Goseong Chemical, and In Woo finds out that Dong Sik and Bo Kyung actually know each other.