It revolves around the mysterious detective Shen Yanzhi. He lives in seclusion in the antique shop "Wangchenju" in an old alley in Jiangnan. He seems indifferent and distant, but he can always discern clues that ordinary people ignore. Rich businessman Gu Qishan was buried in his study. The police determined that it was an accidental fire. However, his son Gu Mingxuan came to the house with a strange token engraved with a crow with a key, claiming that the words in his father's diary, "A crow has a key, old debts must be repaid" were related to the death of his mother twenty years ago.
Shen Yanzhi was involved in this suspicious case. As he explored Gu Zhai's study, he discovered that behind the locked doors and windows and the token that appeared inexplicably, there were secrets buried by time for twenty years. The symbol of "crow with key" seems to involve a more complicated past and entanglements. An old debt and a new case that spanned twenty years were intertwined. Shen Yanzhi peeled off clues in the fog, gradually approaching the truth more terrifying than death, and uncovered the secret past about repayment and redemption in the depths of Qingshi Lane shrouded in rain and fog.
