Moon Lovers: Scarlet Heart Ryeo: Episode 13 is all about testing the loyalty to the king of all the people who lives in the palace. The king is dying of illness and wants the crown prince to return to proclaim son as the next king. The destiny of Goryeo Dynasty lies on Hae-Soo's shoulders leaving her a tough decision whom to choose to entrust the information regarding the king's condition and his request. Hae-Soo sided with So believing that Wook wants the throne for himself.
During the peace gathering, the king is noticeably not comfortable especially when he stood up and eventually fell. He doesn't know that he is going to be killed by Woo-hee disguised as one of the performers. But before she could thrust the weapon to the king, Baek-ah intercepted it and was the one who got stabbed. No one notices since all of the attentions are with the king who fell to the floor.
After the incident, almost everyone was forbidden to visit the king, even the queens. On his deathbed, the king thinks over the accomplishments in his life with Astronomer Choi and Grand General Park only on his side. The two loyal ranked people assured the king that he made the right choice of making the crown prince to be his successor.
Assuming that the king is nearing his death, Yo and Wook conspired to take over the throne by going to the King's palace with an army. They blocked every road to prevent the crown prince from getting inside the palace. So and Wook had a brief fight since the crown prince arrived unexpectedly. It was a plot for Yo to reveal his true intentions of becoming the next king. That is also the time that the death of the king was announced and proclaimed the crown prince as the new king.
Jumping on some scenes, Yo was being chased to death by Wook, So, and their men. So fought with Yo and asked him to give up but he won't until he dropped his sword. So put his sword toward Yo's heart and pushed him off to the edge of the cliff. So made a maneuver and it isn't clear how Yo was stabbed. He then fell off the cliff and was never seen.
The episode ended on Hae-Soo comforting So after he admitted that he stabbed his brother Yo and fell off the cliff. The next episode will shock viewers as Yo returns with a different look and leads an army of rebellion.
