In nineteenth century China, Jungle Village is home to several warring clans. The village blacksmith creates deadly weapons for the clans, intending to use his payments to purchase the freedom of his lover Lady Silk, and leave the village. The region's governor tasks the Lion Clan's leader Gold Lion with protecting a large shipment of gold that must pass through the village. Gold is betrayed by his lieutenants Silver Lion and Bronze Lion, who plan to steal the gold. They use the chaos ensuing from a fight with the Hyena Clan to allow their co-conspirator Poison Daggerthe governor's aideto assassinate Gold, after which Silver becomes the Lions' leader. Gold's son Zen-Yi learns of his father's murder and sets off to the village to seek revenge.
The Emperor's undercover emissary Jack Knife arrives in the village to monitor the gold and takes up residence in the Pink Blossom, a brothel run by Madam Blossom, Lady Silk's madame. Silver sends members of the Rodent clan to kill Zen-Yi before he can reach the village, but Zen-Yi kills them. The mercenary Brass Body arrives in the village and meets with Silver; he is sent to kill Zen-Yi. The blacksmith meets with Silk in the brothel and delivers the final payment needed to free her. After arriving in the village, Zen-Yi and his men are confronted by Brass and find that they cannot physically harm him because his skin turns to metal on impact. Brass beats Zen-Yi and destroys his blade-laden armor. Zen-Yi's last surviving man sacrifices himself to pull a canopy support beam loose, burying Brass under heavy stone. The blacksmith is watching the fight; he rescues Zen-Yi and helps him recover as penance for crafting the weapon that killed Zen-Yi's father.
Meanwhile, the gold shipment arrives in the village, accompanied by two skilled warriors, the Geminis. The Lions soon confront the Geminis and their men, and in the ensuing fight, Poison Dagger assassinates the Geminis and the Lions capture the gold. Jack later arrives to investigate the incident and learns that the Geminis were poisoned with mercury-tipped weapons, leading him to the blacksmith. The Lions' theft prompts the governor to send his Jackal troops to recover the shipment or destroy the village. Zen-Yi asks the blacksmith to craft him a new suit of weaponized armor. The Lions suspect that the blacksmith is helping Zen-Yi and have him tortured for information. The blacksmith refuses to talk, and Brass cuts off his forearms. Jack, who had been following the blacksmith, saves him from bleeding to death. While the blacksmith recovers, he tells Jack of his past as an emancipated American slave who accidentally killed a white man who refused to let him go. He fled America by boat and went to China, where monks trained him to use his body's energy to perform superhuman feats. Jack and the blacksmith craft his greatest weapon: a pair of iron forearms that he can animate using this energy.
Zen-Yi recovers and joins Jack and the blacksmith. Meanwhile, Blossom offers to let Silver hide the gold in a secret tomb beneath the brothel in return for payment. The gold is stored in a coffin which is raised up to the rafters. That night, Blossom has her girls serve the Lions, and Silk serves Brass. At Blossom's signal, the girls use weapons hidden in their mouths to poison many of the Lions, and they join with Blossom as the Black Widows. When Silk tries to poison Brass, his skin protects him, and he beats and almost kills her. Zen-Yi, Jack, and the blacksmith arrive and join with the Black Widows to fight the remaining Lions while Blossom and Bronze fight and kill each other. While fighting Jack, Poison Dagger is crushed between large moving gears. Silver and Zen-Yi fight in the tomb; Zen-Yi cuts the coffin free, and it crushes Silver. The blacksmith finds Silk, who dies in his arms. He confronts Brass, and his iron fists prove capable of inflicting damage on Brass' seemingly invincible body. While Brass is in metal form, a powerful punch from the blacksmith shatters him to pieces. Jack runs outside in time to stop the Jackals from decimating the building with a Gatling gun.
In the epilogue, Jack leaves the village to accompany the gold, and Zen-Yi tells the blacksmith that he has gained a brother. With the clans destroyed and the village safe, the blacksmith vows to keep it that way and destroys the sign pointing to his weapon shop. During the credits, Zen-Yi's pregnant fiancee is kidnapped by a bird clan, prompting Zen-Yi to seek the blacksmith's aid.