After an alleged drug trafficker, Yoo Dae-hun, is found dead, Hyun-jin enlists as an officer of the special investigative unit. She has her suspicions about the case and sights Soo-hyun, a killer disguised as a veterinarian, rescuing wild animals.
Soo-hyun, Hyun-jin and a mysterious high-school girl reside in the same building. Meanwhile, the 'Red Mafia', a Russian mafia is connected to the case Soo-hyun is investigating.
Karimoff escapes Soo-hyun and Hyun-jin, and seeks a window to strike back. The man-behind is slowly revealed and Soo-hyun's memories begin to return and Karimoff holds Seul-gi hostage.
Karimoff escapes Soo-hyun and Hyun-jin, and seeks a window to strike back. The man-behind is slowly revealed and Soo-hyun's memories begin to return and Karimoff holds Seul-gi hostage.
Soo-hyun recalls a memory from childhood and visits an orphanage. Meanwhile, Hyun-jin starts to look into Seul-gi's traumatic past and becomes aware of her identity.
Hyun-woo recalls Jae-hwan's ambition and closes in on his neck tightly. Soo-hyun finds trouble and faces a divided path.
Soo-hyun questions the identity of his client, and threatens Phillip to source the information. Hyun-jin is placed on security detail and Soo-hyun assassinates Hyun-jin's client.
Soo-hyun learns of the terrible actions of Jae-hwan, and is confused. Soo-hyun uses Phillip to draw out his client as his memory slowly returns.
Soo-hyun chases the hard truth, and is forced to accept it as he learns of his past. Meanwhile, Do Jae-hwan is suspicious of Ji-hye and all plans are put at risk.
Soo-hyun tracks Ji-hye and crosses paths with Hyun-jin. Hyun-jin is attacked by an unidentified crew. Soo-hyun identifies his client.
Ji-hye disappears along with the secrets of the serial murder. Hyun-jin frantically searches for Ji-hye. Meanwhile, Hyun-jin learns of the relationship between Soo-hyun and Do Jae-hwan, and takes a step closer to Soo-hyun's identity.
Soo-hyun's identity is revealed to the police putting him on the run as a killer. Soo-hyun waits for an opportunity to kill his last target, but Hyun-jin begs him to stop.