Chen Yan, 42 years old, is the ace detective of the former city's criminal investigation detachment. Because the investigation of the "Lin Family Extermination Case" was blocked three years ago, he voluntarily applied for transfer to the old city police station. On the surface, he lived a decadent life, but in fact he secretly pursued old cases. He is good at observing micro-expressions and restoring the logical chain of crime scenes. He is sensitive to smells and sounds, and has mild obsessive-compulsive disorder. Partner Lin Xi, 28 years old, graduated from a prestigious university with a major in criminal investigation. He was transferred to the old city because he refused the request of his superiors to "revise the case report". He is impulsive but has keen observation. At first, he was dissatisfied with Chen Yan's "lay down" attitude, but later discovered his hidden strength and became his assistant and trusted partner. "Snake Scale Mark" A snake scale pattern painted with special paint will appear at the scene of all cases, and it is exactly the same as the mark at the scene of the "Lin Family Extermination Case" three years ago, implying that the series of cases are related to the old case.
