In 3000 AD, Jonnie Goodboy Tyler, Barry Pepper, lives in the Rocky Mountains with a hardy band of cave-dwellers who fear the “demons” that rule Earth. Jonnie doubts their stories and rides into the lowlands, where hunters Carlo, Kim Coates, and Rock, Michel Perron, reveal to him a desolate, overgrown city. While exploring the ruins, he is captured by the demons, a cruel alien race called Psychlos, and taken as a slave to a base hidden beneath a vast dome that sustains a breathable atmosphere for the occupiers.
Terl, John Travolta, the planet’s high-born Earth security chief, notices Jonnie’s growing resolve and becomes intrigued. After a supervisor informs him that his temporary Earth assignment will be extended as punishment for offending a politician, Terl hatches a plan with his assistant Ker, [Forest Whitaker](/actor/forest Whitaker). They know of a recently exposed gold deposit in a radiation-heavy zone. Gold is valuable to the Psychlos, and their losses from mining have mounted, so Terl and Ker intend to train humans to mine the gold and use part of it to bribe his way off the planet.
To accelerate Jonnie’s assimilation, Terl puts him into a learning machine that rapidly teaches Psychlo language and technology. Jonnie secretly shares his new knowledge with the other slaves while concealing it from Terl and Ker. After an initial escape attempt fails, Terl brings him to the Denver Library, hoping to prove that human knowledge is no match for Psychlo power. Jonnie reads the Declaration of Independence and grows inspired to not only escape but to imagine reclaiming his world.
Jonnie’s fiancée Chrissy, Sabine Karsenti, is captured while searching for him and fitted with an explosive collar. Terl uses the threat to coerce Jonnie, and he also makes an example out of a fellow slave, Sammy, Sylvain Landry.
Believing the slaves are subdued, Terl coldly blackmails the planet administrator to authorize the mining operation. Jonnie receives further training to pilot aircraft and is sent to the mining site with a team. He splits the group—half pretend to work while the other half covertly arms themselves, seizing abandoned human weapons and hauling gold from Fort Knox to pass off as legitimate mining output. Ker attempts to blackmail Terl for a bigger share of the gold, but Terl detects the gambit and shoots off Ker’s hand.
The revolt erupts as humans strike the base, using Harrier jets to counter the Psychlo defenses and explosives to rupture the dome. Terl orders the execution of all humans and warns the Psychlo homeworld to teleport an extermination force. As the teleporter activates, Jonnie confronts Terl, reattaches Chrissy’s collar to his arm, and tricks him into detonating it. Sammy’s brother Mickey, Andrew Campbell, rides the teleporter to the Psychlo homeworld with a nuclear weapon, and the ensuing fallout incinerates the atmosphere, triggering the planet’s explosion.
Back on Earth, at Fort Knox, Jonnie taunts a captive Terl, signaling that surviving Psychlos will pay any price for their schemes' collapse. Ker agrees to teach Psychlo technology to the humans, sharing in the newly forged power as they move toward a future shaped by their hard-won rebellion.
