Two boys from the same school are murdered. In their stomachs there are capsules containing scraps from a diary that describe the next victims. Suspecting there might be the possibility that a killer is at the same school, detective Chu Ja-young (Shin Eun-kyung), with her rookie partner Kim Dong-wook (Eric Mun) search the school to find identical handwriting that matches that of the diary excerpts. When they finally find the matching one, they’re told that Jin-mo, the student who wrote the text, has died already in a car accident one month previous. As Ja-young and Dong-wook discover Jin-mo’s secret diary, more clues are revealed concerning the next victim. They also discover that Jin-mo was bullied by his schoolmates, and that there is a darker secret to be revealed.