Several years after he was forced to retire during an investigation into a gruesome killing, former police officer turned security guard Zhang Zili suspects a possible link with another spate of murders. It seems all the victims had been in a relationship with one woman, Wu Zhizhen. With the help of an old colleague, Zhang sets out to solve the case. As he inexplicably begins to fall in love with Wu he discovers innocence and guilt are not so easy to assess.