Detective Jun-mo goes undercover within Gangnam Union to probe an international drug trade.

Barely passing Gi-cheul's test, Jun-mo joins Gangnam Union and discovers an unexpected truth.

Eui-jeong's appearance puts the squad in trouble. Gi-cheul finds last night's attack suspicious.

The team seeks Eui-jeong's aid to assist Jun-mo in a crisis, which leads to a perilous love triangle.

Earning Gi-cheul's trust, Jun-mo becomes anxious as he sees Gi-cheul making a move towards Eui-jeong.

The delivery accident jeopardizes the trade. Detective Hwang closely surveils Gangnam Union.

Hae-ryun shows interest in Jun-mo and Eui-jeong approaches Gi-cheul. Jun-mo takes an extreme measure.

Gi-cheul suspects Jun-mo. The four people's irreversible decisions trigger the biggest crisis.