It is set in a futuristic realm within a high-tech adult amusement park known as Delos, which features a tripartite structure comprising WesternWorld, MedievalWorld, and RomanWorld. Each zone is designed for guests to fully immerse themselves in scripted experiences by interacting with highly advanced androids that are crafted to emulate humans convincingly, albeit with slight imperfections in their hands. Visitors to the park are encouraged to indulge their every whim, including the capability to lethally interact with these androids, all while paying a hefty sum of $1,000 a day for the thrill.
Among the guests are Peter Martin (Richard Benjamin), a newcomer eager for adventure, and his seasoned friend John Blane (Brolin), who has frequented the park before. Upon entering the WesternWorld, they are introduced to one of the park's most captivating features: the Gunslinger (Yul Brynner), a robot meticulously programmed to engage in gunfights. The design ensures that in a duel, a human will always best the Gunslinger, as the weapons assigned to guests operate with temperature sensors that prevent them from harming other living beings while allowing them to "kill" androids.
As the experience unfolds, the technicians overseeing Delos start to witness alarming malfunctions within the androids. In a pioneering depiction of a computer virus in cinema, they discuss the erratic behavior of machines spreading "like a disease" through the different realms of the park. Initially, the malfunctioning robots are limited to MedievalWorld, where a robotic rattlesnake venomously strikes Blane. Increasingly uncanny incidents unfold; notably, a female android rejects a guest's advances, marking the beginning of inexorable breakdowns. The chaos culminates when a robotic Black Knight fatally injures a guest during a skirmish in MedievalWorld. In a desperate bid to restore order, the park's supervisors attempt to shut down power across the facility, inadvertently trapping themselves in the control rooms without the ability to restore the systems while the androids begin to wreak havoc.
Unaware of the catastrophic shift in their surroundings due to their inebriation after a bar scuffle, Martin and Blane are jolted awake by the presence of the Gunslinger, who issues a deadly challenge. Initially dismissive, Blane finds himself victimized as the robot shoots him dead. In pure survival mode, Martin flees from the relentless pursuit of the Gunslinger, navigating through the chaotic aftermath where panicked technicians and lifeless bodies fill the park’s halls.
Desperately, he escapes into an underground maintenance area that leads to overwhelming devastation affecting the park team, most of whom have suffocated due to the ventilation shutdown. The Gunslinger relentlessly tracks Martin down through the dark corridors, leading him to the robot repair facility. In a moment of cunning, Martin uses a beaker of hydrochloric acid to ambush the bot, believing he has put an end to its threat. Yet, the reality is far grimmer. Even after sustaining severe damage, the Gunslinger persists, its face distorted but functional as it adeptly navigates using modified infrared sensors.
As Martin makes his way into MedievalWorld, he inadvertently creates a distraction that allows the Gunslinger to pinpoint his whereabouts once more. In a final confrontation, armed with only a torch, Martin seizes a fleeting chance to set the deadly machine on fire. Although he initially believes he has vanquished the foe, the horror continues when he discovers that a captive he freed is nothing but a robotic replica. The charred body of the Gunslinger remains hazardous yet, until it ultimately falls and is rendered powerless.
In the chilling silence that follows, Martin becomes the apparent survivor of this technological nightmare, seated on the dungeon steps, grappling with the stark irony of Delos's promotional mantra: “Have we got a vacation for you!”
