Because of middle schooler Cheon-ji’s unexpected suicide, her mother Hyun-sook and older sister Man-ji are driven out of their home and move to another apartment. By chance, Man-ji hears a story that might relate to the suicide after meeting her dead sister's friends. Tracking down clues, Man-ji discovers that Cheon-ji's best friend, Hwa-yeon is behind all the events that happened. While seeking for the secret behind her sister's death, Man-ji finds out that Cheon-ji left notes in red knitting balls.