Ji Sung, an NIS agent, is enraged and turns desperate after his colleague gets killed in Hong Kong after chasing Wang Wei. On the flight back, Ji Sung steals Wang Wei's passport. Subsequently, Wang Wei faints, swallowing a pill. Do Kyung says she'll pose as his fiancee, but Ha Jun, the monitoring team leader, asks her to go through immigrations. Ji Sung keeps an eye on Do Kyung walking to the transit area instead of immigrations. Later, Do Kyung and Ji Sung get arrested for a drug case.

Incheon Airport goes into an emergency state due to Wang Wei. Ji Sung asks Do Kyung and Ha Jun for help, claiming Wang Wei isn't a typical illegal alien. While searching through the baggage screening area, Ji Sung finds Wang Wei running toward the runway and a fierce chase takes place.

After taking shots at a work function, Do Kyung gets sick and Ji Sung helps her. In the process, the two talk and learn about each other. Later, Ji Sung demands that the airport raise the security level for an industrial spy at his first meeting with the airport authority and the board. Despite Do Kyung's resistance, the security level gets raised, causing delays for passengers. Being blamed for the commotion, Ji Sung finds a Triad pendant on the neck of a man who may be the spy.

After missing Charlie, the suspected industrial spy and underboss of Triad, Ji Sung lashes out at Do Kyung. Ha Jun scolds him for being harsh, but Do Kyung says she understands Ji Sung. Meanwhile, Do Kyung surprisingly bumps into Charlie. After a quick encounter, Do Kyung runs to get help but gets held hostage by Charlie. Watching the event at the monitoring room, Ji Sung rushes to the site and faces Charlie.

After a suicide attempt of the daughter of North Korea's top politician, the hospital becomes a special security area, and the NIS bans any access. This creates conflict within operation headquarters. Myung Woo hears from Hye Ryeon that she entered illegally to meet her lover, and she asks Ji Sung to help her. However, Ji Sung coldly refuses to. Meanwhile, Do Kyung freezes when she sees Yi Kyung, but she turns away and leaves. Later, Do Kyung looks for Yi Kyung again while Yi Kyung watches.