Shi-Hyun (Jung Kyoung-Ho) grew up in an orphanage, before running away from there. He then made a living by working as a drug courier and picked up the nickname "Doctor's Son." He's now the boss of a mid-size gang. His drug supplier is a man known as Scale (Kim Byung-Ok). Shi-Hyun has plans take over his position.
Meanwhile, Hyeong-Min (Lee Jae-Yoon) becomes the section chief of a special investigation unit. Their goal is to take down Scale, who killed an undercover officer. Hyeong-Min's girlfriend Kyung-Mi (Ko Na-Eun) is also a detective. She also grew up in an orphanage with Soo-Min (Nam Gyu-Ri). They grew up like real sisters and Soo-Min is now studying to enter the police academy.
While trying to catch Scale, Hyeong-Min learns about a guy called "Doctor's Son." Now, Hyeong-Min and his team go after Shi-Hyun.
