Thread of Lies (2014)

Middle-schooler Cheon-ji's unexpected suicide causes her mother Hyeon-sook and older sister Man-ji to be driven out of their home and into another apartment. Man-ji happens to hear a story that might relate to the suicide after meeting Cheon-ji's friends. Tracking down clues, Man-ji discovers that Cheon-ji's best friend Hwa-yeon is behind everything. Searching for the secret behind her sister's death, Man-ji finds out that Cheon-ji left notes in red knitting balls.