In 1800, the last year of King Jeongjo's reign, he learns through Hwang Yeokgwan that the child to be born between him and Cheongyeon (Kim Sung-rim) will be the light of Joseon, and that its fate is endangered by a swordsman. In his haste, Jeongjo uses a royal secret to open a time portal, makes Cheongyeon flee, and orders the elite guards Ja Un-geom (Lee Gyeong-yeong) and U Un-geom (Kim Min-jong) to protect her. Takagatsu (Dokgo Yeong-jae), a samurai of the Japanese shogun, upon learning of these movements, sends Kanjyo (Jang Dong-jik) and a group of assassins to pursue them. In 1996, Seoul, Kanjyo, knowing that the light of Joseon has not yet extinguished, is lurking for an opportunity to eliminate them on the day of a total solar eclipse.