Shi Hyun 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. Shi Hyun has plans take over his position.
Meanwhile, Hyeong Min becomes the section chief of a special investigation unit. Their goal is to take read moredown Scale, who killed an undercover officer. Hyeong Min's girlfriend Kyung Mi is also a detective. She also grew up in an orphanage with Soo Min. 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.