In the Stone Age, Cang's flint tribe lived on the edge of the Cangmang Mountains for generations. Recently, hunting teams have often lost contact in the dusk. Those who return are either speechless and crazy, or their bodies are full of ulcers and die. In the abandoned ancient ruins on the west side of the tribe, bone whistles are heard every full moon, and the totem patterns on the rock walls quietly shift at night. Cang discovered that black moss remained in the camps of the missing people, and the "underground taboo" that the elders of the tribe kept secret seemed to be closely related to the deep caves under the ancient ruins. There are no fantasy powers, only the survival struggle and unknown fear of primitive tribes. Every step of the investigation is accompanied by a test of life and death, and ancient secrets gradually reveal their outlines in the blood and fog.
