E. E. ‚Doc‘ Smith 
Gray Lensman [EPUB ebook] 

Kimball Kinnison, the greatest Lensman of his day, is on a mission to destroy the dreaded space pirates known as the Boskone. The Boskonians are set on complete conquest of the civilized worlds. Their strongholds are shielded from the Lensman by impenetrable thought screens.
Kinnison is up to the task, but what he doesn’t know is that Boskone’s influence reaches all way into his beloved Galactic Patrol. Will he discover this before it’s too late.
A grand adventure from the father of Space Opera.