### Story Synopsis
- A Recurring Nightmare: On his birthday, criminal investigation captain Ke Chengyu is urgently summoned to the scene of the latest murder. He discovers that the killing closely resembles the methods used in the “Butterfly Killer” cases from three years ago, even though that killer was shot dead long ago.
- The Butterfly Returns: The new victim bears the same butterfly mark and semen evidence found in the old cases, but DNA testing shows that the sample does not match the dead killer, suggesting either a copycat or that the real culprit is still out there.
- Expert Assistance: Criminal psychologist Wen Yulu joins the task force. She quickly picks up on the ritualistic quality of the killer’s methods and the psychological projection behind them, and suspects the killer is using murder to “create” some kind of artwork.
- A Hidden Connection: Ke Chengyu discovers that all the victims were connected to an underground club called “Metamorphosis,” which seems to have some link to the killer convicted three years ago.
- Personal Shadows: Ke Chengyu is forced to confront the possibility that he made a mistake when he shot the killer three years ago. Meanwhile, Wen Yulu shows an unusual fixation on the case. The secrets they are each hiding gradually come to light.
