Masters of Space
Author: first_name:  Edward Everett
last_name: Evans
first_name: E. E.
last_name: Smith
Language: English
Year: 1961

The Masters had ruled all space with an unconquerable iron fist. But the Masters were gone. And this new, 
young race who came now to take their place--could they hope to defeat the ancient Enemy of All? (Summary by Gutenberg)