In 15th-century Joseon, King Se Jong (Han Suk Kyu), a visionary monarch, dreams of creating a more equal world for his people, especially after his father’s brutal regime before him. However, his radical pursuit of "Hangul," an accessible alphabet, faces fierce opposition from Confucian scholars who aim to stop the king by any means necessary – even if it means murder. At the same time, Kang Chae Yoon (Jang Hyuk) and So Yi (Shin Sae Kyung), former slaves who survived the prior king’s massacre, have both found ways into King Se Jeong’s court, but have very different end goals in mind. Will King Se Jeong find a way to spread literacy across the nation despite fierce opposition from multiple sides?