Descendants of the Sun

Yoo Si-jin (Song Joong-ki) is a captain in the South Korean Army's special forces. He and his friend, Master sergeant Seo Dae-young (Jin Goo), are off-duty when they witness a young man stealing a motorcycle; they apprehend him using toy guns they had been using for a shooting game. The thief, Kim Gi-bum (Kim Min-seok), gets injured during the chase and is therefore sent to the hospital. Dae-young realises his cell phone was stolen by the thief and goes to the hospital with Si-jin to retrieve it. In the emergency room, Si-jin meets Dr Kang Mo-yeon (Song Hye-kyo) for the first time and is instantly attracted to her. Mo-Yeon mistakenly assumes Si-jin is part of the thief's criminal gang after overhearing Dae-young address him as "Big Boss", which is his call sign. Si-jin proves his identity with the help of army surgeon Yoon Myung-ju (Kim Ji-won), who turns out to be Mo-yeon's former rival from medical school. Si-jin and Mo-yeon begin to date, but due to Si-jin often being called in for duty, their dates are often interrupted halfway. Si-jin receives orders to be deployed on a peacekeeping mission in the fictional war-torn country of Uruk. Meanwhile, Mo-yeon is upset because she found out that she had been passed over for a professorship favouring a less-capable colleague who had familial connections to the hospital management. When Si-jin returns and meets Mo-yeon again, she directly asks him to explain his sudden disappearances and the nature of his job. Still, he cannot go into too much detail due to the highly classified nature of his assignments. They talk about their views on life and realise how different they are. Si-jin, as a soldier, kills to protect lives, while Mo-yeon, as a doctor, honours the Hippocratic Oath and tries to save lives. Due to their philosophical differences, they agree to part ways. Dae-young, on the other hand, faces a dilemma over whether to continue his relationship with Myung-ju or risk being forced out of the army for breaking fraternisation rules as he was not a commissioned officer. The fact that Myung-ju is the daughter of his and Si-jin's superior, the commander of the Special Forces, makes the situation even more fraught. Eight months later, Mo-yeon rebuffs the romantic advances of the hospital director and, as revenge, is assigned to lead a team of medical volunteers to Uruk against her will. In Uruk, Si-jin and Mo-yeon reunite and both gain a deeper insight into one another's jobs as their respective teams endure an earthquake and an M3 virus (fictional disease described as being deadlier than ebola) outbreak, while also dealing with a local warlord who once fought alongside Si-jin in a joint mission between the South Korean and United States armed forces but now takes advantage of the corrupt government of Uruk to make money off human and arms trafficking. While in Uruk, Mo-yeon accidentally confesses her feelings (much to the amusement of their respective teams) and the two officially start dating. She gradually comes to terms with the possibility of Si-jin's being killed in action and the fact that she may never have full disclosure of his whereabouts. In the meantime, the usually stoic Dae-young finally works up the nerve to show more affection toward Myung-ju after she nearly dies in quarantine after being infected with the M3 virus. Si-jin and Mo-yeon continue their relationship after returning to Korea, until Si-jin and Dae-young are sent on a classified operation in which they disappear and are assumed to be dead. Months pass during which Mo-yeon mourns Si-jin's death and sends him text messages that she presumes he cannot read. She decides to commemorate the one-year mark of his passing by volunteering with a medical team sent to Albania, where Si-jin finds her toying with a pebble they had picked up from a beach. Later, Mo-yeon's colleagues in Korea mistake Si-jin for a ghost over a face call because Mo-yeon has laid the table in front of him with traditional jesa foods she had been meaning to put out for his memorial. Meanwhile, Dae-young heads to Uruk to find Myung-ju, who has been deployed there alongside the thief Si-jin and Dae-young apprehended who has now risen through the ranks to take Dae-young's former position. After their reunion, Si-jin tells Mo-yeon that he and Dae-young were rescued from captivity by "a friend from afar", a soldier from North Korea whom Si-jin had helped before. Si-jin and Mo-yeon, along with Myung-ju and Dae-young, are all happily reunited with each other.