In 1873 New Mexico Territory, a man (Daniel Craig) awakens injured in the desert with a strange metal bracelet attached to his left wrist and no memory. He wanders into the town of Absolution, where preacher Meacham (Clancy Brown) treats his wound. Sheriff John Taggart (Keith Carradine) recognizes the stranger as wanted outlaw Jake Lonergan and attempts to arrest him. Jake nearly escapes, but a woman named Ella Swenson (Olivia Wilde) interferes. Taggart and his men prepare to transport both Jake and petulant young drunkard Percy Dolarhyde (Paul Dano) to Santa Fe for trial.
Percy's father, Colonel Woodrow Dolarhyde (Harrison Ford), a ruthless cattle baron, arrives with armed men and demands Percy be released. He also wants Jake, who has stolen gold from him. During the standoff, alien ships begin attacking the town. Percy, Taggart, and other townsfolk are abducted by long, whip-like feelers hanging from the bottom of the ships. Jake's bracelet inexplicably activates and transforms, becoming a weapon; he shoots down a ship, ending the attack.
Dolarhyde, Ella, and other townsfolk form a posse to track an injured alien that escaped from the downed ship. Meanwhile, Jake travels to an abandoned cabin and, in a flashback, recalls returning to it with stolen gold and then being abducted, along with a woman named Alice, by the aliens. His memories returning, Jake joins the posse. During the evening, they come upon a capsized paddle wheel steamboat that the aliens apparently dumped far from any large river. They camp inside it; during the night the alien kills Meacham, who sacrifices himself to save Emmett, Taggart's grandson.
By morning, most of the posse has deserted, and Jake's former gang attacks the rest. Jake, who stole the gang's loot after their last heist, attempts to retake control but is foiled. The aliens attack again and abduct Ella. Jake jumps aboard the ship and attacks the alien pilot, causing the ship to crash in a river. The pilot survives the crash and attacks Ella, fatally wounding her, before Jake kills it with his wrist-blaster.
The remaining posse is captured by Chiricahua Apache Native Americans, who blame them for the alien attacks. After Ella's corpse is dumped on a fire by a Chiricahua warrior, she is resurrected and emerges from the fire. Ella reveals herself to be from another alien race, who had traveled to Earth to help resist the invaders after they destroyed her home world. The aliens - who are mining gold and abducting people to conduct experiments on them - have superior weaponry and are far stronger and more durable than humans; only Jake's wrist weapon or a well-aimed round from a rifle can kill them with a single shot. Ella tells them that the previous attackers were just scouts.
She also claims Jake holds the secret to the aliens' whereabouts and argues that they must defeat the aliens before the invaders exterminate all life on Earth. After taking medicine offered by the Apaches' medicine man, Jake's memory returns. He recalls watching Alice get vivisected and euthanized; he escaped by stealing the bracelet encasing his wrist. He also remembers the location of the aliens' base of operations: their landed mother ship.
With this knowledge, they plan to attack the alien base. Jake leaves to persuade his old gang to join the fight while Dolarhyde takes command of the original group and the Apaches. After the combined groups maneuver the aliens into a ground battle, Jake and Ella board the ship and free the captives, but Jake is captured. Dolarhyde rescues him, and both men escape from the ship after killing the alien responsible for Alice's death. The ship takes off as the remaining aliens flee Earth, but Ella stays on board to end the threat: she sacrifices herself by entering the ship's core and turning Jake's wrist weapon into a bomb; it detonates, obliterating the ship.
With the aliens gone, the rescued townsfolk begin remembering their pasts. Still a wanted man, Jake chooses to leave; the sheriff and Dolarhyde decide to claim he was killed in the invasion. The citizens intend to rebuild their town.
Daniel Craig as Jake Lonergan, an amnesiac outlaw.
Harrison Ford as Colonel Woodrow Dolarhyde, a powerful cattleman
Olivia Wilde as Ella Swenson, a mysterious traveler who aids Lonergan.
Sam Rockwell as Doc, the town's doctor and owner of Absolution's local saloon
Paul Dano as Percy Dolarhyde, Woodrow's trouble-making son.
Clancy Brown as Meacham, Absolution's preacher
Keith Carradine as Sheriff John Taggart, Absolution's sheriff.
Noah Ringer as Emmett Taggart, John Taggart's grandson.
Adam Beach as Nat Colorado, Dolarhyde's Native American right-hand man.
Abigail Spencer as Alice, Jake's lost love.
Ana de la Reguera as María, Absolution's saloon maid and Doc's wife.
Walton Goggins as Hunt, a bandit and friend of Lonergan.
Julio Cedillo as Bronc, a Mexican bandit.
David O'Hara as Pat Dolan, Lonergan's former gang-member.
Toby Huss as Roy Murphy
Raoul Trujillo as Black Knife, the Chiricahua Apache chief.
Paul Ortega as Apache Medicine Man
Wyatt Russell as Little Mickey