Kim Jongin was assigned to protect the princess. She put her trust in him to bring her to safety. But along the way, the princess realizes she would forever be in danger because Jongin is full of secrets.

Yejin has already fallen for Kai but he isn't interested in having a girlfriend, despite his flirtatious nature around Yejin. When he can no longer deny his feelings, he makes a promise with her. The only question is who can keep this promise and who can't.