The X Factor

"Diskan Fentress was a mutant. And when he could no longer bear the shame of being an outsider among his own people, he stole a spaceship and jumped to an uncharted, frozen planet. There Diskan met the alien Brothers-in-Fur, who led him to the galaxy ruins where long ago a great civilization had ruled..." (Source: Back of Del Rey / Ballantine edition, 1984)