After the sudden death of her father, seventeen-year-old Lin Yue moves with her mother to Susu Villa, a quiet residential community where they hope to leave their painful past behind and begin again. With only a few months left before her senior-year graduation, Lin Yue believes the new environment will give her the peace she needs to focus on school and prepare for her future. But Susu Villa isn't as peaceful as it seems.From the moment Lin Yue arrives, she notices strange things. The residents are unusually reserved; everyone seems to mind their business, and certain questions are met with uncomfortable silence. Her mother also behaves strangely, refusing to explain why parts of the building seem familiar to her. At first, Lin Yue tries to ignore the uneasiness. Then she begins noticing two suspicious men watching her. Soon afterward, she learns about Su Wan, a young woman who mysteriously disappeared from Susu Villa five years earlier. There was no sign of forced entry, no clear evidence of kidnapping, and no body. The case eventually went cold, leaving behind only rumours and unanswered questions. But there is one detail that continues to haunt the residents.Su Wan disappeared from Room 407.Lin Yue becomes curious when she discovers that Room 407 supposedly no longer exists. On the fourth floor of her building, there are apartments 405 and 406, but where Room 407 should be, there's only a blank wall. The more Lin Yue investigates, the stranger it becomes.She receives anonymous messages from someone who appears to know far more about her than a stranger should. Photographs begin appearing in places where they shouldn't be. Someone warns her to stop asking questions. At night, Lin Yue hears footsteps and knocking coming from behind the wall where Room 407 is supposed to be.Then she discovers an old photograph. In it, her mother is standing behind Su Wan. The discovery forces Lin Yue to question everything she thought she knew about her family.Why did her mother know Su Wan?Why did she never tell Lin Yue about their connection?And why does Lin Yue have the unsettling feeling that Susu Villa isn't entirely unfamiliar?As Lin Yue searches for answers, she begins uncovering fragments of a mystery that has been carefully buried for years. Every answer leads to another question, and every person she trusts seems to be hiding something.Her new classmate Han Qiao becomes one of the few willing to help her investigate, but even Han Qiao seems to know more about Susu Villa than she admits. Meanwhile, the people watching Lin Yue become increasingly bold. The warnings become more personal. The clues become more disturbing. And Lin Yue begins to wonder whether she moved to Susu Villa by coincidence or whether someone wants her there. She begins to suspect everyone around her, even her friend Han Qiao. The mystery surrounding Room 407 deepens, Lin Yue uncovers the truth before the secrets of the past catch up with her, but not without a cost, because Room 407 may not simply be the place where a girl disappeared. It may be the place where Lin Yue's own forgotten story began.