When Lee Kyung-mi (Go Na-eun) is murdered by drug lords, her mentee and friend Yoon Soo-min (Nam Gyu-ri) is recruited by Kyung-mi's boyfriend (Lee Jae-yoon) to try and catch the prime suspect, a mysterious figure only known as "The Doctor's Son" (Jung Kyung-ho). In a fateful encounter, Soo-min falls for The Doctor's Son, not realizing who he is. Unbeknownst to her and every other police officer, The Doctor's Son is also an undercover agent. Working under the orders of police director Min Hong Ki (Son Chang-Min), The Doctor's Son works to take down the Busan drug ring and seek revenge against the dealers who were responsible for his mother's drug addiction.