Season synopsis
Contains spoilers for this season and earlier seasons.
Special-forces captain Yoo Shi-jin and surgeon Kang Mo-yeon are attracted to one another, but secret missions and their differing duties frustrate their first attempt at dating. They meet again in fictional Uruk, where she joins a medical team and he commands soldiers. An earthquake brings both groups into a rescue operation at a collapsed power plant. Mo-yeon must choose which of two trapped men can be saved, while Shi-jin resists a contractor’s demand to recover hidden diamonds. Sergeant Seo Dae-young and army surgeon Yoon Myung-joo also reunite, despite her father’s opposition to their relationship.
The relief work exposes child trafficking and the criminal operations of David Agus, Shi-jin’s former comrade. An M3 virus outbreak infects Myung-joo, and Agus seizes the medicine before kidnapping Mo-yeon. Shi-jin’s team recovers the treatment and rescues the captives; he kills Agus when the man reaches for a weapon. Mo-yeon accepts the dangers of Shi-jin’s work. Back in Korea, an operation involving North Korean officer Ahn Jung-joon leaves Shi-jin critically wounded. Mo-yeon saves him, and he helps Ahn expose a traitor through a recorded confession.
During a later three-month mission, Shi-jin and Dae-young are presumed killed in an explosion. Their farewell letters devastate Mo-yeon and Myung-joo. A year later, Mo-yeon is volunteering in Albania when Shi-jin’s voice comes over her radio. Dae-young returns to Myung-joo in Uruk. Both men survived captivity and were rescued by Ahn before their execution. Myung-joo’s father finally approves her relationship with Dae-young without requiring him to leave the army. At Daniel and Ye-hwa’s wedding in Canada, a nearby volcanic eruption sends the reunited friends toward another relief effort.