Hidden Root falls apart as traitors abound. Chae Yun goes on a desperate search to save So Yi.

Desperate to know what the Solution is, Jung Gi Joon is willing to give up his position as a leader of Hidden Root in order to bring Sejong down.

The final showdown begins as Jung Gi Joon readies for his assassination attempt against Sejong. So Yi struggles to pass down her knowledge of the Solution.