In a post-apocalyptic future (2293) the world is divided between the Eternals (immortals) and Brutes (mortals).
After killing Arthur Frayn and hiding inside the floating head "Zardoz", Zed (a "Brutal Exterminator") travels to Vortex, the place inhabited by the Eternals.
Upon his arrival in Vortex, Zed is made a slave. But later the eternals discover that Zed is the near-perfect by product of a eugenics experiment orchestrated by Arthur Frayn (Zardoz).
Zed later uncovers the truth of the eternals and their ways and sets out to change the world.
The movie begins with Arthur Frayn (Who at this point calls himself "Zardoz") introducing himself as a man who wishes to die, but he says it is no longer possible because he is immortal.
There are some kind of birthing/re-animation chambers similar in appearance to those in The Matrix and one of the characters mentions a "third death" hinting that a person has been either re-animated or re-born. It's not made clear whether this is some kind of cloning technology or a kind of biological backup system.
During one scene, One of the characters asks Zed (Sean Connery's character) if he; "Would like to see immortality at work?". The 2 men arrive at an old folks home like area where the geriatrics have been "shunned" and The character mentions that they live a life senility. This is clearly a more negative/dystopian or deathist view of immortality, and one that would not be well thought of by longevity advocates.
We learn that the Eternals get their immortality from an AI known as the Tabernacle.
There are also various retro-futuristic and futuristic technologies shown throughout the movie including holographic devices and hydroponic-like plant growing devices.
Zed is also revealed to be the result of a Eugenics experiment.