Among the dwindling survivors of a small mountain village is a frustrated young man called Jonnie Goodboy Tyler. The villagers know of no other people besides themselves and are gradually sinking into savagery, dying off from a mysterious weakening disease. A strapping and keen-minded youth, Jonnie stands out among his people. At 20 years old, he is half a head taller than the average villager, a muscular six feet and shining with the bronzed health of his outdoor existence. His corn-yellow hair and beard contrast with his ice-blue eyes.

Fed up with watching his people succumb to hardship and disease, Jonnie decides to violate long-standing taboos about leaving the village. He determines to ignore the legends about the monsters said to have been sent by the gods to punish man and he steels himself even against the pleas of his beloved girlfriend, Chrissie, who fears for his life. Jonnie strikes out on his own to discover what has happened to mankind and to find a better place for his people to live.

In the plains below his mountain home, Jonnie and his horse, Windsplitter, encounter the myths come to life: evil beyond all legend, and truths beyond imagining.

Captured by the alien Psychlos, Jonnie soon learns that the fate of man is certain extinction unless he can find a way to fight the unstoppable. Determined to overcome his ignorance of the world and the universe, Jonnie sets out to learn all he can from the Psychlo overlords. Despite imprisonment, enslavement, abuse and overwhelming odds, Jonnie conceives a daring plan of rebellion to defeat the Psychlos and drive them from Earth. But it will take allies, and where will a lone human find them?

Chrissie lives in the mountain village with Jonnie and the handful of inhabitants who remain amongst the crumbling huts and the horses and dogs. She is a slight girl, very pretty, eighteen years old. She has large black eyes in strange contrast to her corn-silk hair.

Independent and strong-willed, she wears little more than a thin doeskin wrapped tightly around herself, which hugs her attractive form to advantage.

Chrissie loves Jonnie and there is no one else as far as she is concerned–no matter what the others in the village say about this rebellious and determined young man.

Reluctantly accepting Jonnie's decision to go on his search, Chrissie nonetheless pledges that she will come after him herself if he does not return to the village within one year. Legendary monsters or no, Chrissie has her own inner strength and her devotion to Jonnie makes her capable of any bravery. But if Jonnie does not return, will Chrissie walk into the same Psychlo clutches that ensnared him?

In the midst of Terl the Psychlo's secret plan to enrich himself using "man-animals" as slave labor, Jonnie Goodboy Tyler learns of another tribe of surviving humans, living in a land still known as Scotland.

Recruited as laborers, a contingent of hardy Scottish highlanders are really the allies that Jonnie will need to mount his bold assault on Psychlo dominance over the Earth. Under Jonnie's leadership the band forges a bond of strength and determination as they struggle through a spectacular and dangerous mining project high on a cliff in the Rocky Mountains.

Among them is Robert the Fox, an elder veteran of many raids and one of the only humans besides Jonnie who has ever seen a Psychlo and escaped to tell about it. To the Scottish, Robert the Fox is a respected chieftain, a wise and brave warrior in the best Scottish tradition. To Jonnie he will become a true friend and vital ally. With the loyalty of Robert the Fox comes the faith of the Scottish highlanders, who trust his judgment and military skills enough to follow him and Jonnie on the most desperate and crucial campaign ever fought on Battlefield Earth.