Hyun-sook (Kim Hee-ae) is a widowed single mother who is raising two teenage daughters while working at a big grocery store. One day, her youngest child, 14-year-old Cheon-ji (Kim Hyang-gi) suddenly commits suicide by hanging without even leaving a note. To Hyun-sook and her older daughter Man-ji (Go Ah-sung), Cheon-ji was the sweet child of the family who rarely complained and studied hard, while always trying to comfort her hardworking, often-weary mother. Struggling with guilt and anger, and not knowing why Cheon-ji chose to kill herself, the two women wonder whether there was something they missed or something they could have said or done. Flashbacks of Cheon-ji's past show that she had been the victim of cruel acts of bullying at her middle school, led by Hwa-yeon (Kim Yoo-jung), the prettiest and most popular girl in class whose true callous and manipulative nature hides a tortured soul.