Zheng Ke, the number one assassin in the world, who went to the palace to prepare to assassinate his father in order to avenge his death. However, he never imagined that a huge conspiracy was about to be revealed. Zheng Ke, who was dormant in the palace, accidentally exchanged bodies with Qi Wan Er, the princess who was loved by thousands of people. So, the two began to look for a way to switch back together. As their understanding deepened, the two went from being suspicious of each other to protecting and understanding each other, gradually strengthened their feelings for each other, and worked together to overthrow the conspiracy of the prime minister who attempted rebellion...