Copperhead

Wild Bill rides onto a battlefield and encounters an elderly Mexican who asks 'Qué pasa aqui?'. He answers with 'La Serpienta Del Diablo'. He approaches a carriage, a woman falls out, a copperhead slithers out, and Bill shoots it before riding away.

The next day Bill arrives in a New Mexico town and asks for John Murphy at the local saloon. The bartender Garrett tells him Murphy is dead. A cowboy named Jesse demands a poker game, while Jesse's men hold Bill at gunpoint as he warns that a swarm of snakes is headed for the town. The confrontation ends with Jesse shot in the chest and Bill wounded in the arm as the others intervene to stop the fight.

Josiah patches Bill's arm, and they discover the horses and Henry in the stable have been killed by the snakes. The snakes attack the saloon, killing several patrons and forcing the town to fight back. Bill's horse collapses in the chaos, and he shoots it to spare it from further suffering.

Bill tells Sheriff Mercer to arm every available weapon in the town. Will, his girlfriend Jane, and saloon girl Darla help herd women and children into the bank safe for safety. Tannen unveils a Gatling gun and a flamethrower salvaged from the war, and the group digs a pool to corner the snakes.

At night the snakes launch a fierce assault on the town while the defenders hold the line in Murphy's room and the saloon. Tannen is killed as the defense tightens around the survivors. Bill, Will, Roscoe, and Ponce hunt through Murphy's room to uncover a bloody clue: Murphy's bed bears evidence and a gold watch reveals a disturbing truth. Ponce is killed by a snake at the window, and Bill and Will realize Roscoe murdered Murphy and lock him in a room.

Snakes begin crawling through the floor and the walls toward the hotel. Will and Garrett fetch dynamite from a shed in the alley and use it to clear a path, even killing a snake hiding behind a door. They also improvise by square-dancing on another snake to slow it down as the danger closes in.

With the danger escalating, Bill hands Will his gun and Will detonates the dynamite to devastating effect, destroying many of the approaching snakes. Garrett and Jane shoot with pistols and a shotgun, aiming at the creature’s weaknesses. The giant copperhead finally collapses after Bill shoots it in the back and then the mouth, but Mercer is crushed when the beast closes in on him.

The Pinkertons arrive in town, looking for Bill. Garrett reveals to them that Bill is Murphy. Bill warns that there are women and children locked in the bank safe and the Pinkertons go inside to rescue them as the group makes a quick escape on horses. Ms. Murphy finds her father's gold watch and, in the fading light, sees Bill riding away into the sunset.

Bill, Will, Garrett, Jane, and Josiah seize the Pinkertons' horses and ride west toward Lincoln as the pursuers close in. They use teamwork to slip through the chase and keep ahead of their pursuers. The film hints at a long journey ahead as they disappear across the plains.

In a final, quiet moment, Bill rides off toward the horizon on his horse, leading the group into an uncertain future. The silhouette of a lone rider fades against the setting sun as the story closes on the open plains.