Set in Youcheng, an old riverside city in southern China, the story follows Shen Yan, a former deputy captain of the criminal investigation squad who was forced to resign after an unsolved case three years ago. He opens the Yanzhi Detective Agency, taking on bizarre cases the police cannot get involved in. Youcheng conceals eerie places such as century-old underground waterways, abandoned Republican-era mansions, sealed-off ancient villages, and secret psychiatric hospitals. Each case seems unrelated, yet they all point to the Red-Cord Strangling Ghost case Shen Yan failed to solve three years ago. After thirty cases, a shocking conspiracy hidden throughout the city is revealed.
