The Legend follows Hwanwoong, the 19th king of Goguryeo, who falls in love with Saeoh and gives her the joojak necklace. However, Kajin becomes jealous and throws Saeoh's son off a cliff.

Saeoh, thinking her son is dead, turns into the black joojak to destroy the world. Hwanwoong must stop her, and later prophecizes the coming of Joo Shin's true king. The series premiered in South Korea.