Marshal Bravestarr and a female judge are sent to New Texas, a frontier planet under attack by the evil cattle spirit Stampede, who, with his ruthless sidekick, Tex Hex, are vying for control of the universe, one planet at a time.
When rare mineral that can produce incredible amounts of energy is discovered on a mostly uninhabited planet called New Texas, settlers and frontiersmen as well as outlaws arrive from all over space to find fortune. However, what they don't know is that a monstrous demonic spirit called Stampede, who looks like a bull, also lives there. Stampede puts feared outlaw Tex Hex under his control and starts collecting various dangerous outlaws for its supernatural army of minions that will take over the planet. Scared citizens send for help, so a highly capable Native American marshal called BraveStarr and a feisty, pretty and always fair female judge J. B. McBride arrive to investigate the attacks. BraveStarr soon finds allies - a wild alien sentient semi-anthropomorphic warhorse called Thirty-Thirty, who carries a powerful shotgun, a funny member of an alien mole-people race, who are master diggers and builders as well as the original natives of the planet, and a mysterious powerful Native American shaman, who is the only one who knows about Stampede, and who gives BraveStarr the power of the eyes of the Hawk, which enhances his vision, the ears of the Wolf, which gives him super-human hearing, the strength of the Bear, which gives him super-human strength and the speed of the Puma, which gives BraveStarr super-human speed. Even with all this powers and sidekicks, though, taking down Stampede could prove to be impossible.
The story is set in a distant future, where humanity has apparently colonized various planets. The film opens with a conflict between the good Shaman of a space-faring Native-American tribe and a demon-like entity called Stampede. As revealed in flashback, the previous battle between them had destroyed a planet and had isolated them from their former allies. Moments before the battle, Shaman decides to send his only companion, the young boy Bravestarr, to the Marshal organization for training.
Stampede causes the Shaman's spaceship to crash-land in the desert planet of New Texas, in an attempt to kill him. The Shaman uses much of his power to survive the event, and he somehow prematurely ages in the process. He emerges from the crash-site as a weakened old man. Stampede realizes that he will need a servant to continue his campaign.
On another area of New Texas, the mining partners Tex Hex and Angus McBride have had a falling out. Tex Hex incapacitates Angus and plans to leave the planet with their spaceship. It is loaded with a valuable mineral resource, Kerium, which will make Tex wealthy. Angus warns him that the ship is overloaded and can not escape the planet's gravity, but Tex refuses to listen. Shortly after, the overloaded spaceship crashes in the desert and Tex is seemingly killed.
Stampede resurrects Tex Hex, and performs a ritual which grants Tex magical powers of his own. The process leaves Tex with a withered appearance, while his hair and mustache turn white. Tex is now powerful, but looks much older than his actual age. Meanwhile, Angus has been crippled (permanently losing the ability to walk), but manages to contact a space-faring rescue ship to take him off the planet. Its crew discover the Kerium and start spreading the news.
The film covers events of the following decades through brief scenes. Like a gold-rush, the search for Kerium causes miners, merchants, and outlaws to flock to New Texas. As a town emerges in the desert, Tex Hex progressively recruits the most skilled of the outlaws into his gang. Some of them he convinces to join by promises of great wealth, others he defeats in combat and then intimidates into joining him.
New Texas has had no law or legal system, but it eventually requests for interplanetary marshals and judges to be send. The authorities from the other civilized world only send them one marshal (BraveStarr) and one judge (J.B. McBride, Angus' daughter). BraveStarr is quite charmed with the young, red-headed J.B. J.B. is intrigued when she discovers that BraveStarr has superhuman powers, but he explains that he can't control his powers or when they appear.
BraveStarr and Tex Hex introduce themselves to each other, shortly after the marshal's arrival. BraveStarr gets the upper hand in their initial skirmish, but then Tex outsmarts him and captures him. BraveStarr is soon stranded in the desert, while J.B. impulsively enters the desert to search for him.
BraveStarr is rescued by the Shaman, who helps him to regain lost memories of his childhood. The Shaman used a ritual which allows BraveStarr to gain control and awareness over his powers. Meanwhile, J.B. gets lost in the desert and befriends the planet's only native tribe, the Prairie People. They grant to her a combat suit and weapons created by their ancestors.
Following the return from the desert, BraveStarr uses his new powers to defeat Tex in unarmed combat. Tex feels that his gang lacks the numbers to overcome BraveStarr and his allies. Tex sends recruitment offers to every outlaw and villain on the planet, and soon has a large army at hand. Stampede does not appreciate Tex's initiative and uses intimidation to remind Tex that he is still the demon's servant, and not a general. Stampede, however, promises to help Tex in the upcoming battle.
BraveStarr and his allies rebuild the town in order to make it able to endure a siege. BraveStarr decides to recruit the Prairie People to help rebuild the town, despite the disdain which most of the town people feel for them. The racist mayor voices objections, but BraveStarr and J.B. intimidate him to back down.
As J.B. prepares herself to take part in the coming battle, she admits that she keeps thinking whether she will survive to see "another sunrise". BraveStarr admits to her that he is afraid too, but that it is natural to feel that way when facing death. They exchange their first kisses shortly after.
During the actual battle, BraveStarr and his allies outclass Tex's army of outlaws, and even manage to capture a few of their enemies. But then Tex summons Stampede, who overcomes the town's defenses. Stampede uses necromancy to raise skeletons of giant beasts from the desert, and has them attack the town. Stampede then defeats the Shaman in combat. But BraveStarr uses the Shaman's magic spear to deliver a seemingly mortal wound to Stampede. The demon vanishes and Tex Hex is sucked into a portal.
With the town actually surviving the battle, BraveStarr leaves it to spend time with the Shaman. J.B. seems disappointed that her lover is leaving her behind. She is pleasantly surprised when he returns moments later, to explain that the two of them are leaving together. The film ends.
