Woo Jin takes care of his son Ji Ho alone after his wife Soo A passed away. Before she passed away, she promised she would be back on a rainy day one year later. One year later, Soo A appears again, but she does not remember anything.

Two apathetic police academy recruits who become best buddies through the tough training together witness a woman being abducted right before their very eyes. As they were taught in the academy, they quickly report the incident to the police, but the police are in no hurry to jump on the case. So the duo decide to take the matter into their own hands and rescue the woman.

Set during the Silla dynasty, Sam Maekjong is the son of the fallen king and present queen regent, Jiso, but he has been kept in hiding for protection ever since he was a young boy, when his father was murdered. Over the years the powerful nobles have tried and failed to usurp power from Jiso, causing her to grow wary and later even reluctant to hand the throne over. As her son comes of age, she creates the Hwarang, an elite group of male youth who train in fighting and education. Their existence cuts across the existing power factions and Sam Maekjong is amidst their ranks under the false name Kim Ji-Dwi, unbeknownst to other Hwarang members.

Woo-Jin changes into a different person when he wakes up. He falls in love with Yi-Soo.