Hyeon-sook (Kim Hee-ae) is a single mother raising two teenage daughters while working at a grocery store. One day, her youngest child, 14-year-old Cheon-ji (Kim Hyang-gi), suddenly commits suicide without even leaving a note. This comes as a shock to Hyeon-sook and her older daughter Man-ji (Go Ah-sung) since Cheon-ji was a sweet child, who rarely complained and studied hard, while always trying to comfort her hardworking mother. Struggling to understand why Cheon-ji chose to kill herself, the two women wonder whether there was something they didn't know about Cheon-ji's life. As Hyeon-sook and Man-ji unravel Cheon-ji's quiet life, they come to realize that she had been the victim of brutal bullying at her middle school, led by Hwa-yeon (Kim Yoo-jung), a troubled, manipulative teenager.