Before her wedding, Shen Zhiyi received a text message from her late father: "Do not marry Gu Chengze, go check C-17." Her husband's concealment, her mother's secret, and her best friend's pain all point to a covered-up old case from twenty years ago. The anonymous person "Codename A" guides step by step, with truth and traps intertwined. When the evidence surfaces, the 7th household dies, and the next household is -01. Under the truth, no one is innocent.