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.

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.

The battle with Jae-geon creates a crack. Jun-mo joins forces with Hae-ryun to resume the trade.

Jun-mo and Eui-jeong juggle duty and feelings. Hwang continues to meddle, and the final day arrives.

An accident halts the trade and a crisis approaches as Eui-jeong and Do-hyung worry about Jun-mo.

Gi-cheul and Jun-mo make their way to the final deal. Korea, China, and Japan prepare for the arrest.