Synopsis：On their way home from school during their senior year of high school, twin sisters saw a blood-soaked cloth fall from an abandoned building. Driven by curiosity, they entered the building, intending to play the role of "beauty saves the hero," but instead discovered a girl chained up with iron restraints. Before they could rescue her, footsteps approached from downstairs. Yet in the end, why did the twin sisters turn on each other, with only one walking out of that building? Was the one who died the elder sister or the younger? What could have driven the twins to commit such brutal violence? Years later, the surviving twin has kept this dark secret buried deep in her heart. Where is her sister's body? The suspects include her college professor, a mysterious online forum moderator known as Feng Hen, and a university roommate who was once as close as a sister. One by one, they begin to unravel the secret she has tried so hard to conceal.