Shen Mo, the chief catcher of the Six Doors, has been investigating the case for ten years and has never seen such a contradictory death situation:
Cheng Xiaotian, the leader of the Iron Sword Sect, was stabbed directly into the heart with a sharp blade. He died miserably, but a strange "smile" was stitched out of the corner of his mouth with red thread.
The deceased was not killed by a knife, but died of "ventricular ice crystal" - a poison that has long been lost in the Western Regions.
The only clue at the scene was that the vague "Huang Quan Yin" fragrance belonged to the demon doctor from the Western Regions who was sent to prison by him personally - Bai Zhi.
In order to survive, Bai Zhi in prison readily accepted Shen Mo's deal: "Help me reverse the case and I will help you detoxify."
One is the cold-faced King of Hell who will do anything for order, and the other is a crazy and poisonous doctor who treats human life as nothing.
As the two men investigate further, they discover that behind the so-called "Iron Sword Sect Extermination Case", there are shocking secrets about the Fire Lotus Sect twenty years ago.
What Shen Mo didn't know was that the "Shuangtian Jue" he used to solve the case was exactly the thing that Bai Zhi tried every means to retrieve to destroy the family.
And the "red thread" that sutured the corners of the deceased's mouth was tightening towards their necks inch by inch...
Intention: Destiny is a blade, trust and dependence are mutual; in the abyss of lies, only each other is the true salvation.