A true historical drama about King Sejong, the greatest ruler in Joseon history who sought to enhance national prosperity and military power through astronomy, and Jang Yeong-sil, the most remarkable scientist.

In the 15th century, despite so many accomplishments he has made for the people, King Sejong, his biggest goal is still remaining; the invention of original letters that can be read and written by all the people. But courtiers who want to dominate the knowledge and the power, are against his will and discourage his belief. Frustrated King Sejong hears about a bonze Sinmi a phonogram expert, and secretly brings him in the palace.

During the reign of King Sejong in the 15th century, the Joseon Dynasty was the embodiment of the perfect state. To the Ming China, the aspiring imperial power, Joseon presented an obstacle to territorial expansion. To protect themselves from war, King Sejong develops a secret weapon to defend their territory and take back their land and supremacy.

The movie depicts the three months before Choong-nyung (the future Sejong the Great) becomes king. The Annals of the Joseon Dynasty, which follows the history of the Joseon Dynasty between 1413 and 1865, leaves out records of this crucial period. While future generations would come to know him as King Sejong, the legendary figure who created the Korean alphabet and advanced the country’s scientific research and law, Prince Choong-nyung was originally dismissed as a reclusive bookworm. When his older brothers Yangnyeong and Hyoryeong fail to impress their father King Taejong, the king makes a royal command for Choong-nyung to become the next ruler of the kingdom instead.