The Butterfly Murders

Fang Hongye, initially an outsider, is invited to Shen's Family Fort to investigate a series of murders. The investigation unfolds through his dual role as participant and observer, shaping how the truth emerges. This invitation pulls him deeper into a web of secrets within the Jianghu world.

The film introduces Hongye's Notebook, a handwritten record of peculiar martial-arts events. The eight pages describe a mysterious killer butterfly incident at the fort, linking a string of deaths to these insects. Later it is revealed that these pages are forgeries designed to manipulate rivals and the martial world.

Decades earlier, the killer butterfly murders claimed the previous fort owner during a tomb robbery. The deaths are tied to the strange butterfly motif that haunts the fort. This sets a pattern that drives current investigators to seek the truth behind the murders.

Decades after the initial murders, another tomb raider dies in a similar manner, prompting Shen Qing, the fort owner, to invite Hongye, Tian Feng, and Qing Yingzi. The team arrives to unravel the connection between the butterflies and the deaths. Tension builds as the past collides with the present.

With the investigators' arrival, the butterfly murders escalate, claiming more victims until Shen Qing himself falls to the killer butterflies. The deaths raise alarm across the martial-arts world and put pressure on solving the mystery quickly. The sense of urgency intensifies as the killer operates within the fort.

Shen Qing's wife insists on waiting for the arrival of the three brothers, the 'Four Phases of Heavenly Thunder,' before taking action. This hesitation adds to the tension and delays direct confrontation with the killer. The family dynamics show how strategy and ritual influence the course of events.

The mute servant Ah-Zhi leads Hongye to a secret gunpowder storage room, raising suspicion about hidden weapons. The discovery hints at a deeper conspiracy and the fort's secret projects. The gunpowder cache becomes a crucial clue for the investigators.

The three brothers arrive as scheduled, coinciding with Mrs. Shen's mysterious death by an iron-clad figure. This figure is later revealed to be Shen Qing himself, who is Yu Zhen, the deceased fourth brother of the 'Four Phases.' The revelation reframes the entire investigation.

Six years earlier, Yu Zhen established the Shen's Family Fort to secretly develop an alloy for gun-barrel weapons. After completing the weapon, he orchestrated the butterfly murders and forged Hongye's Notebook to eliminate rivals and dominate the Jianghu. He used Tian Feng to unwittingly assist him.

As the investigation climaxes, Hongye uncovers Yu Zhen's true identity as Shen Qing and the manipulation of Tian Feng. The forged notebook and butterfly murders are exposed as a grand scheme to orchestrate power and eliminate competitors. The truth redefines trust among the investigators.

With the mastermind unveiled, Hongye solves the case and chooses to leave the fort behind. His exit marks the end of his internal narration and the end of the fort's haunting secret. The resolution underscores his dual role as participant and observer.

In a final confrontation, Yu Zhen (Shen Qing) and Tian Feng, along with others, perish in a fierce battle. The fort is destroyed along with the weapon the mastermind built, ending the threat once and for all. The legacy of the butterfly murders is concluded with the fort's ruin.