An early paperback cover painting by Jones. "In a world of alien creatures, he searched for the secret that could save the Earth"

From the back cover:

The Throne World

Here was the center of the great intergalactic empire that held Earth in thrall. Here dwelled the humanoids known as the High Born, as superior to Earthlings as men were to infants. And here reigned their Emperor, Oran, all-wise, all-powerful. James Keil was brought to the Throne World for the High Borns' pleasure. To them he was a Wolfling, an amusing pet. But Keil had his own reason for being here--to discover the flaw in their invincibility, and destroy their hated tyranny...