Seven years after the notorious kidnapping and murder case in Vietnam, the criminals have finally been apprehended. Ma Seok-do, an irreplaceable detective known for his fierce reputation and played by Ma Dong-seok, has been promoted to the Metropolitan Investigation Unit of the Seoul Metropolitan Police Agency. One day, after resolving a violent altercation, he and his new team members take on a murder investigation.

During the process, Ma Seok-do uncovers a connection between the case and a new type of drug, prompting him to push for an intensified investigation. Following the trail of evidence, Ma and his team manage to arrest two operatives from a Japanese gang, seize 20 kilograms of narcotics, and recover a stolen police handgun. However, as team leader Jang Tae-soo and two officers transport the suspects and confiscated drugs to the station, they are ambushed by an unknown group. The attack leaves Jang Tae-soo and his team unconscious from their injuries, while the two gang members are killed and the seized drugs are stolen.