The Tale of Nokdu S01 E28 Dong-Ju Stands Before the King

"Mischievous gisaeng in training has a suspicious mother."

The revolting army takes over the castle. Everyone seems to be after the King, but the King himself just realizes that his trusted royal guard Yeon-Su is actually Nok-Du. Enraged with betrayal, the King goes out in the middle of the night to search for Nok-Du.