The X Factor by Andre Norton
Diskan Fentress, mutant son of a space explorer, felt himself out of place on the luxury worlds of civilized space. It was not until he stole a space ship and a travel key to the unexplored planet of Mimir that he first felt his latent powers to be of some worth. For Mimir was a world of strange relics, of beasts that were not beasts, and of a ruined city whose shadows spoke of a higher and weirder civilization than any the galaxy had yet discovered. And it was to fall to Diskan's lot to meet The X Factor head on - and to settle a planet's fate with his reaction.
Paperback, Mass Market
Condition: Very Good (scuff on front cover, yellowing)
Publisher: Ace, 1965