John Russell Fearn Dwellers in Darkness: The Golden Amazon Saga, Book Fourteen

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Voyaging into a sector of interstellar space that is plunged into total darkness with an absolute absence of any light, the four Cosmic Crusaders encounter their most powerful and sinister enemy yet--an alien mastermind who is regarded as a God by the race he has created. This scientist has altered the nature of space itself, so that it no longer conducts light, forcing the slaves he's created to evolve without eyes, and to develop extrasensory perception. Not content with shaping the evolution of their bodies, the mastermind also contrives an apparatus that impresses on their minds the need to conquer and dominate, thus creating a menace to the universe that the Crusaders must try to eliminate. Another rousing adventure in this long-running science-fiction adventure series!