In 19th century Asia, a warrior named Yang is part of the Sad Flutes clan, which is considered to be the most cruel assassins ever. His goal is to become the greatest swordsman in the entire world is accomplished when he kills the person who held the title of world's greatest swordsman and leader of an enemy clan. Yang killed every member of the clan, except a little baby girl he comes upon. He spares her and decides to watch over her. This makes Yang an enemy of his own clan, and he is a wanted outlaw in his own homeland
Lynn gives Yang the nickname Skinny and agrees to teach him how to do laundry. He begins to enjoy his life in town, enjoying things he never knew of as a warrior. He becomes friendly with the townspeople, while the baby, named April, is loved by all. He even develops an interest in opera after Lynne shows him on a gramophone. She reveals to him that Smiley taught her a little bit about sword fighting and the Sad Flute clan. She wants yang to teach her more, and asks about the Sad Flutes name. He explains to her that it describes the sound of blood coming from your victim's slit throat, and he is hesitant to teach her the skills of the sword. Meanwhile back in the East, Yang's former clan is shown to be hunting for him. His former Saddest Flute and his ninja army take the same boat to America. Saddest Flute declares that to find Yang in such a large country, you have to wait and listen.
One day, Yang sees Lynne placing flowers on a grave. He asks Eight-Ball about it and he explains that 3 years ago, when Lynne was a teen, the town came under siege by a corrupt Colonel. His preference to rape women with healthy teeth prompted him to choose Lynn as his victim while her father was held to the ground, mother and baby, and brother forced to wait outside. When Lynne was brought to the Colonel in a kitchen, she manages to escape him by throwing a pan of potatoes frying in grease on his face. She runs outside and he shoots her through the chest. Her father struggles to get free and is also shot dead by the Colonel, while her mother, holding her brother runs over and both are killed.
When the townspeople found them and buried them, they found Lynne still alive. Since then, she has made it her goal to avenge the murders. She wants to learn how to fight and kill, and practices throwing knives. Yang surprises Lynne by showing her that her knife throwing is halted slightly by her sight, not her arm, and he gives her a successful lesson by blindfolding her. She is clearly falling in love with Yang and gives him a charm necklace that belonged to her mother.
Yang continues to live his life peacefully in town with April until Christmas rolls around. When the townspeople are celebrating, Yang and Lynn go to the desert to 'dance' in their swordplay. That's where he tells Lynne that she has not won until her enemy's heart stops. Lynne kisses Yang on the mouth, catching him off guard. She runs away, smiling at him, and he sits down, shocked, staring at his lips in the reflection of the sword.
Eight-Ball and other carnies tie Lynne in a cellar for her own good. Yang removes her blades, agreeing with the carnies. She manages to free herself with a concealed knife in her boot. The Colonel has the Latina woman's daughters cleaned up to be raped, but Lynne, disguised as a prostitute, offers herself instead. She fools him, thinking she will be able to kill him when he reveals he recognized her after smelling her neck. His men rush in to hold Lynne down to bed. While back in the laundry, the carnies run in looking for Lynne and Yang knows where she is. He grabs an iron and shatters the seal on his katana to free it. Far awy, Saddest Flute jerks up from meditation, sensing the seal break, and is aware of Yang's location.
The day comes and the Colonel arrives with men to charge the town. Yang stands across from his flower garden, waiting. As they approach, they are met with explosions. From miles away on the Ferris Wheel, Ron is sniping sticks of dynamite hidden in the garden as they come. Yang rapidly and stealthily disposes of the men. The outlaws are lured to the ferris wheel where Yang and the carnies ambush them. Ron slides down to safety on a cable, after which the wheel is destroyed, killing many of the Colonel's men. Thinking it's safe, the carnies come out, only to be attacked. The Colonel's men chase the carnies into the center of town where the Sad Flutes appear out of nowhere. Saddest Flute instructs them to kill. Yang looks to Lynne holding April and tells her to run. The carnies manage to get away before the bloodshed between the ninjas and outlaws.
The Sad Flutes pursue massively, and most are fended off with machine gun fire, but the outlaws are unable to stop Yang, who brutally kills them. He comes into the room to find the Colonel holding a gun to April's head and leaps up to slice the barrel of the gun in half mid-firing. Catching April from falling, Yang steps aside to let Lynne fight the Colonel. After a tense fight, Lynne manages to finally drive a sword through his back. Yang and Lynne exit the room to find the Saddest Flute sitting across the carnage at the end of the hall. He tells Yang that April is the enemy, and asks if he would ever tell April that Yang killed her parents, her whole clan and observes that Yang ran away from his old life of killing to kill more. He says Yang does not belong there. Yang claims he does and will not kill April. Yang and Saddest Flute go to the desert in the sunset and duel to the death. During flashbacks, it shows Saddest Flute training yang as an adult in pouring rain, drilling him through adolescence in snow, forcing child Yang to kill the puppy he was given, declaring Yang's biggest enemy would be his heart, and that as an assassin, he must kill what he loves. He then cuts Saddest Flute's throat.
Jang Dong-gun as Yang
Geoffrey Rush as Ron