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.

Soo-hyun's intertwined past with Seul-gi is revealed as he rescue's her but the memories torment her. Meanwhile, Hyun-jin searches for a connection between the victims.

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.