In a dystopian future, society is divided into the immortal Eternals, who live in a technologically advanced utopia called the Vortex, and the mortal Brutals, who dwell in the desolate Outlands. The Brutals are controlled by the giant stone head of Zardoz, which delivers weapons and commands them to kill each other to maintain population control. Zed, a Brutal Exterminator, grows suspicious of Zardoz and manages to infiltrate the Vortex by hiding inside the stone head. Once inside, he discovers that the Eternals are a decadent and emotionally detached society, maintaining their immortality through advanced technology and shunning all forms of violence.

Zed encounters Consuella and May, two of the female Eternals, who have differing views on his presence; May is curious about him and seeks to understand his genetic potential, while Consuella sees him as a dangerous threat to their way of life. As Zed learns more about the inner workings of the Vortex, he becomes entangled in power struggles and begins to realize the truth behind Zardoz and his own origins. His presence disrupts the status quo and sets off a chain reaction that challenges the very foundation of Eternal society.