E. E. Doc Smith 
Skylark of Valeron 

The incredible starship Skylark Three has fought the Fenachone Supermen to a standstill, and Richard Seaton has gone back to his first love — exploration. Roaming the galaxy, he discovers a world of disembodied intelligences; a world of four dimensions where time was insanely distorted and matter obeyed no terrestrial laws, where 3-dimensional intellects were barely sufficient to thwart invisible mentalities! Meanwhile, the villainous Du Quesne is allying himself with the remnants of the Fenachrone, and planning his next attack . . .