The powerful Psychlos control a vast star empire stretching throughout the universe and encompassing countless worlds. Their invincible military equipment and superior technology makes them the absolute masters of their conquered planets and of subject populations who survive Psychlo dominance.

Physically, the humanoid Psychlos stand an imposing nine feet tall, weighing about a thousand pounds and boasting strength enough to snap a man in half with the talons of a single paw. The Psychlo's face is humanlike but heavy with expressive bones around the mouth and eyes in place of facial hair. Their eyes are amber orbs which seem to glow with menace.

Ravenous for the resources vital to the engines of their empire, the Psychlo Intergalactic Mining Company sets up its massive minesite installations on captured planets like Earth, to bore out of them their precious metals and rare minerals. The mining products are teleported back to the planet Psychlo to feed the insatiable hunger of the core. Consumers and exploiters, the Psychlos see a planet like Earth as nothing more than raw materials, its inhabitants a mere nuisance to be exterminated without a second thought.

Adapted to the heavy gravity of the Psychlo homeworld, Psychlos are also dependent on a highly potent gas for their respiration, forcing them to wear "breathe-gas" masks and tanks when they venture outside the pressurized domes on an "air planet" like Earth. This gas is explosively reactive with uranium, making this radioactive substance one of the few dangers of any kind which Psychlos must avoid.

Dedicated to domination and cruelty, the Psychlo culture is filled with subterfuge, treachery and intimidation. In all they are a monstrous presence against which any resistance seems futile.

Like a nightmare demon conjured from shadows outside the firelight in Jonnie's old village is Terl, the Psychlo, who will dominate Jonnie's existence and alter the fate of Earth.

Psychlo Security Chief for the mining operations of Planet Earth, Terl likes to see himself as important but in reality seethes at the waste of his talents on this insignificant backwater of a planet. He hates Earth and the feeling of exile, stuck in a dead end where there is no opportunity for profitable advancement. Terl is sick of the green hills, blue skies and the weak, poisonous atmosphere which requires him to wear a breathe-gas mask to survive outside the Psychlo domes. He yearns to return rich and powerful to the comforting dark purple hues of his home planet of Psychlo, but he knows that his career is heading towards damning and permanent obscurity.

Clever and manipulative, Terl's mind is as formidable as his brutal strength. Using blackmail and threats to lay the groundwork within his mine site base, Terl sets in motion an elaborate plan to rescue himself from the wretched Earth and seize an illicit fortune. To accomplish his goal, he embarks on a hunt to capture some of the remnant "man-animals" still straggling in a few remote corners of the empty planet. As his trained pets and slaves, they will do his work for him. And then the last of them will be destroyed, as Terl retires to his reward.

His first captive is Jonnie Goodboy Tyler. Terl considers his slave a rat-brained animal. Though the human may nurture foolish doomed hope, the Psychlo security chief is always a chess game ahead of the man-animal, manipulating Jonnie's mind and emotions with heartless calculation. Even as Jonnie plots fiercely to escape, he is only playing into Terl's mighty taloned claws. Terl is a mastermind, who misses no detail. And the man-animals will never be more than tools in his plan.

But as Terl may learn, to underestimate Jonnie Goodboy Tyler—and the hope and will of the human spirit—could be a fatal mistake, even for a Psychlo....

A mining engineer assigned to the same mine site as Terl, Ker is unlike the others of his race, somehow lacking a true devotion to cruelty. Terl uses Ker to teach the animal Jonnie Goodboy Tyler to operate Psychlo mining equipment, but doesn't count on the two forming a kind of friendship.

Ker develops a grudging interest in Jonnie, and eventually answers many of the inquisitive animal's questions about Psychlo operations. In time, Ker comes to look upon the small man-animal as a mining "shaft-mate" and the two explore the possibility of mutual trust.

But in the midst of the evil culture of the Psychlos, Ker's sympathies are aberrant. And Terl is watching, suspicious of everyone. If the security chief discovers even the hint of an alliance between the two, their deaths will quickly follow.

“But more important, the novel is as fun to read as those movies were fun to watch.”

Baltimore Evening Sun