Noori Kim, an eighteen-year-old girl, happened to attend school in place of Chayeon Hong, an eighteen-year-old 'BOY.' But soon... she was caught by Seokyoung Lim, her classmate. To her surprise, Seokyoung promises to keep her identity a secret. As they spend more time trying to keep Noori's secret, their feelings grow beyond that of just friends. Between finishing the mission succesfully and being with Seokyoung as her true self, what choices will she make?