1873. Arizona. Gunslingers Zeke Taylor and Verity Jones are hired to protect a caravan heading to Silver City, which is rumored to have a big silver mine, from the Apache Indians. The caravan is indeed attacked and Taylor and Verity are overpowered by the Indians led by the warrior Warhawk.
Zeke escapes and attempts to find help, but is overpowered by three Indians. As they're about to execute him, a Alien spaceship crash-lands nearby. Its tripulants, crocodile-like Alien conquerers, discover that Earth is not in their registers and decide to take over it, calling in reinforcements. The Indians attempt to make contact and are killed by the Aliens, who make their way to a fort, where they establish a headquarters. Zeke decides to scavenge the crashed spaceship and finds Microwave-emmiting pistol.
Zeke reunites with Verity and they make their way to Silver City alongside the surviving miners, but find the city deserted, save for a few people, led by the Mayor, who reveals that the mine is already empty and many left following this discovery. The group is attacked by a squad of Aliens in flying motorcycles, and Zeke is able to shoot some of them down with the pistol. Verity also finds a whip-like Alien weapons and starts using it. However, they are eventually outnumbered and chased to a gorge, where they are rescued by Warhawk and the Indians, who kill the Aliens with poison-tipped arrows.
The Cowboys and the Indians decide to help eachother to fend off the Aliens. The Indians find cillinders that, once added to their arrows, allow them to shoot miniature atomic bombs. Warhawk also finds a pair of goggles with X-Ray vision, telescopic vision, microscopic vision and infrared vision. He sees Verity bathing alongside some Indian women and falls in love.
The group is approached by the Alien General's shapeshifting female aid, who is tired of her race's ruthless ways and decides to aid the humans in defeating them. Zeke falls in love with her.
The heroes then divise a plan: A group led by the Mayor will fake a direct attack to the Aliens while a second group infiltrates Silver City, which is being used by the Aliens as a operations central, trough the empty silver mines and ambush the creatures, destroying their antemn and preventing them from calling reinforcements. However, they are betrayed by the Mayor, who warns the Aliens in hopes of his life being spared. The Alien General kills the Mayor and captures the heroes, who are prepared to be executed.
Suddenly, the Aliens are ambushed by the Indians, who infiltrate the fort with horses that are able to fly due to horseshoes created from the scraps of the flying motorcycles by the town's blacksmith. The Aliens are killed by the atomic arrows and Zeke confronts the General while Verity and Warhawk fight his second-in-command.
The General wounds Zeke's girlfriend before Zeke uses the pistol to melt some metal that falls on the General, making him so heavy that the floor beneath him cracks and he falls on a makeshift catapult built by the female Alien. She jamms a explosive on the General's chest and catapults him against the antemn, where he explodes, destroying the antemn and dying. The shockwave causes the church's bell to fall on the second-in-command, crushing him before he can kill Verity and Warhawk.
Zeke kisses the female Alien as she dies. Verity and Warhawk also kiss. Zeke discovers that there's a resistence of shapeshifting aliens that want to destroy the evil Aliens, and the his girlfriend was a part of them. Before dying, she radioed her friends and told them that the humans are a good addition to the resistence. Suddenly we see the shapeshifting Aliens on a space station on the Moon using Earth slang such as "Howdy".
THE END... OR IS IT?