A wandering swordsman and swordsmith is escorting his sect's legacy—a black iron sword blank—when he is unexpectedly drawn into an elaborate switching scam. As a mountain healer, a tea-shed owner, and a traveling peddler join the investigation one after another, clues such as oil traces in the bamboo grove, a wooden box under the bridge, and wax molds in an old sword workshop gradually piece together the truth. They discover that what the culprit truly covets is not the sword blank, but the Flame-Stabilizing Crystal that can keep the furnace fire steady. Facing traps, bait, and layer upon layer of scheming, they dismantle each plot and protect the furnace, leading to a final showdown atop the cliff. In the end, greed is defeated by evidence and justice; the wrongdoer lays down his weapon and chooses to atone through action, bringing this martial-world conflict to a bright conclusion.