Invaders From the Infinite

The alien spacecraft was unbelievably big, extremely powerful, and probably irresistible. It came from nowhere and landed on Earth, inspiring everybody with fear. But its aim was not to conquer but to ask for a help! First contact was a job for the excellent 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 them back! John W. Campbell's book is a true