Edmond Hamilton 
Outside the Universe 

‚Spaceships in their thousands, and they’re attacking us! They’ve come from somewhere toward our galaxy – have come out of intergalactic space itself to attack our universe!‘ The Interstellar Patrol, that fabulous fleet manned by all the assorted races of our galaxy, faced its greatest struggle when that alarm came through. For this was an attack from OUTSIDE THE UNIVERSE, a vast migration from another galaxy, and it had to be stopped if a thousand worlds were to survive! This terrific classic space novel on the grandest scale involves three giant galaxies in an all-out conflict.