Se Won was able to speak with his sister Shin Yool because of Wang Wook in this episode. But he never revealed their relationship. Se Won spoke about their mother and insinuating that she looked like her.
The highlight of the episode was in the ending. Se Won was tasked by Sik Ryeom to kill Shin Yool or he will harm the Hwang family. It's either Shin Yool or Yeo Won. The choice is in front of Se Won. But that night, he was inside Shin Yool's bedroom, aiming his sword at her when Wang Wook suddenly appeared and blocked his sword.
The conflict is getting complicated for all the characters.