In the 17th year of the Republic of China, Jinmen. Leng Yue is the most famous detective in the French Concession. He is accompanied by Huang Feihong, a golden-eyed goshawk, who specializes in solving seemingly impossible cases. Mirrored secret rooms, shadow thread murders, breathing walls, human skin sewing - every case is a "secret room built by the human heart."
There is a secret technical genealogy hidden among the nine cases, and when Leng Yue discovers that he is also part of the system, and when the answer he gives becomes the murder weapon to kill the people closest to him, he finally understands: the most unsolvable secret room in the world has never been a room surrounded by bricks and stones.
Nine cases plus the final case, an epitaph about "answers". Under the shell of true reasoning, there is an identity inquiry that lasts for ten years.
