“Sister, we are each other’s only sisters.” Ryu So-hee, a high school student who was seriously ill as a child but has since recovered and is living a normal life, has a younger sister, Ryu Ah-young, who is also ill. Ah-young looks up to her older sister So-hee, but So-hee finds this burdensome. Following a certain incident, their relationship begins to sour, and the sisters grow increasingly uncomfortable with each other. A brutal mystery thriller about sisters unfolding amidst the family’s hidden secrets!