The drama centers on Prince Wang So (Jang Hyuk), who later becomes a king pivotal to Korean history. The story is about how Wang So meets and weds his leading light, Shin Yool (Oh Yeon Seo), the last princess of Balhae.

The narrative begins in 943 AD, with Goryeo’s founder, Wang Geon, still in power as the first king, Taejo. Taejo sees how the jockeying clans threaten the newly unified nation. To counter this, he recalls his 4th son, Wang So, from exile, as his potential heir. Exile has toughened Wang So and taught him to think independently. To help his heir, Taejo plans to wed Wang So to Princess Seo Won (Lee Ha Nui), who has a star-like omen as a birthmark.

Balhae, an empire to the north and east of Goryeo, fell to the Khitans in 926 AD. In the story, Princess Shin Yool is born with a fate to shine for a nation. The Khitans learn this and see her as a threat. They throw baby Shin Yool into an icy river. Her nanny secretly saves her. They flee to China, where Shin Yool grows up to become a successful merchant. But she too has a star-like birthmark.