Su Jing, a female special police officer who retired due to injuries, used all her savings to buy a four-story building in the old city and rent it out. Each of the six tenants is perfect: a model couple, a motivated medical student, an elegant piano teacher, a home-based programmer, and an entrepreneurial boy. Until the whole building starts having "reasonable accidents" - precise accidents that never hurt anyone. Su Jing discovers that all the tenants are hiding the same secret: they were all the "sole survivors" of unsolved cases in the city for ten years, and the murderer is still at large.
