On a rainy night, the master of the ancient quarter dies mysteriously. The doors and windows are tightly locked from the inside; it looks like an accident, but suspicions are deep. Investigators use physical evidence as a breakthrough, starting from subtle traces to dig deep step by step. Undaunted by the fog and seeking verification rigorously, they gradually unravel the complete truth of using inferior goods for huge profits and designing a fake locked room to cover up the crime. Finally, before the night lanterns are lit, they clarify the case, intercept dangerous goods, and protect the safety of the region. The story highlights that justice will eventually arrive, warns against greed and reckless actions, shows that fraud will eventually be exposed, and emphasizes that abiding by the law and keeping a righteous heart is the right path.