The history that we couldn't record.

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.