Waking up in the Joseon Dynasty, a modern transmigrator finds himself in the body of Prince Yangnyeong, the eldest son of King Taejong. Destined for deposition so his brilliant younger brother Chungnyeong can become the great King Sejong, he chooses a different path. Armed with knowledge of the future, he resolves to build the glorious age of Sejong with his own hands, leaving no room for his brother on the throne.