The film introduces Tao Goo (the Weird), Chang-Yi (the Bad), and Do-Won (the Good), who are all aboard a packed train. The Good wants to eliminate everyone bad, the Bad is out for a certain map, and the Weird is just looking for a quick buck. Eventually, through no fault of his own, the Weird gets a hold of the map and the chase is on.
It turns out the map holds the location for an ancient Chinese treasure. The Bad is in constant pursuit, killing almost everyone he encounters. The Good, it turns out, is a bounty hunter in search of Chang-Yi (the Bad) and the Finger Chopper, an old criminal from Korea. The Good suspects Chang-Yi of being the Finger Chopper.
In the climax, the Chinese army, the local gang, and Chang-Yi's gang, all collide while pursuing the Weird. During this scuffle, the Good rides through, killing dozens with handy shots and explosions. The Good, the Bad, and the Weird all meet up for a standoff at the treasure point. Here, Good learns from Bad that the Finger Chopper is actually the Weird, who left Korea for a different life after he unknowingly chopped off two of Chang-Yi's fingers. All three of them shoot each other numerous times. Only the Bad dies. The Good is wounded, and the Weird was wearing a steel plate to stop bullets. It turns out the Weird went to the wrong treasure spot.
At the end, we see the Good in search of the Weird, who is last seen riding off into the desert.