After getting an officer suspended from service, Ryu Soo-yeol gets a step closer to a promotion. Oh Kyung-tae looks for a young girl's missing mom.

Soo-yeol digs deeper into the case, while Kyung-tae is wrongly framed for the murder. Amidst the dilemma between justice and success, following some valuable information received from officer Lee Hee-gyeom, Soo-yeol once again faces the crazy stranger.

Soo-yeol falls from Do Yu-gon's good graces. While searching for the necklace at home, Soo-yeol finds a collection of objects that are not his.

After ensuring Kyung-tae's safety, Soo-yeol pulls a dirty move. With Kim Kye-sik back on the force, the narcotics unit tracks down a street drug.

Soo-yeol searches high and low to prove Hee-gyeom's innocence. But the deeper he dives into the case, the closer he comes to falling into a trap.

Soo-yeol reopens a closed case. He teams up with K to investigate quietly and uncovers the opponent's weakness. Meanwhile, the body count grows.

Soo-yeol and Hee-gyeom shift focus to the head of the drug cartel. Ms. Yong threatens the police to get the seized assets back in her hands.

Soo-yeol learns that K is closely linked to his childhood trauma. A girl shows up at the police station, delirious and covered in someone else's blood.

When bits of his memory return, Soo-yeol re-examines the murder of his father. Finding similar cases, he learns one person was involved in all of them.

As the identity of X comes to light, his deranged schemes pick up pace. He comes between Soo-yeol and K by revealing K's murderous instincts.

Soo-yeol visits Shin Joo-hyuk to seek treatment, but unleashes a very angry K instead. A victim opens up after an attempted suicide.

Soo-yeol's hunt for the truth endangers those around him. He has a final face-off with the crazed killer at the place where it all began.