A husband and wife, both detectives, volunteer to participate in a dangerous mission to stop a drug trafficking organization.
Detective Junmo goes undercover within Gangnam Union to probe an international drug trade.
Barely passing Gicheul's test, Junmo joins Gangnam Union and discovers an unexpected truth.
Euijeong's appearance puts the squad in trouble; Gicheul finds last night's attack suspicious.
Junmo is subjected to another shocking test, and Jungbae begins to doubt him; with Junmo backed into a corner, the team enlists Euijeong to help him; Song Donghyuk's subordinate, Kang Geon, teams up with Sung Kisoo of Jaegeon Group to seek revenge.
Severely damaged by the attack, Gicheul strives to find the traitor within the union; Gicheul begins to make a move toward Euijeong as she joins the investigation team again to help Junmo; he gives Junmo the task of receiving their guests from China.
The delivery accident jeopardizes the trade; Detective Hwang closely surveils Gangnam Union.