A re-imagining of the legendary tale of the troubled father-son relationship between King Yeongjo and his only son Prince Sado. While his father insists on a strong and centralized government, Crown Prince Sado promotes social justice and equality throughout the kingdom. Throughout eight fateful years, the strain on their relationship — both familial and political — eventually evolves into a total breakdown, ending with one of the most tragic stories in Joseon history.

Secret Door ran for 1 season. No new episodes are scheduled.