E. E. Smith 
Gray Lensman [EPUB ebook] 

Space Duel to the Death. Somewhere among the galaxies was the stronghold of Boskone – a network of brilliant interplanetary criminals whose mania for conquest threatened the future o all civilization. But Where? Boskanian bases dotted the universe – shielded by gigantic thought-screens that defied penetration. It was up to Lensman Kim Kinnison, using his fantastic mental powers, to infiltrate the Boskonian strongholds and learn the location of the enemy’s Grand Base – and smash it forever!