Invaders from the Infinite. Arcot, Wade and Morey Book 3

The alien spaceship was unthinkably huge, enormously powerful, apparently irresistible. It came from the void and settle on Earth, striking awe into the hearts of all who saw it. Its burden, however, was not conquest - but a call for the brilliant team of scientists, Arcot, Wade and Morey, explorers of the islands of space. And what they learned was an offer of an alliance against an invading foe so powerful that no known force could turn back.
John W. Campbell's Invaders from the Infinite is a veritable odyssey of the universe, exploring world after world, and uncovering cosmic secret after cosmic secret. Here is a classic novel of super-science that may never be surpassed.