Man is an intelligent mammal. His intelligence lies in his brain. In mammals the tissues of the central nervous system are irreplaceable. The brain contains something like 100,000,000,000,000 neurons, but 100,000 are destroyed on an average day of a man's life. Cosmic rays and general internal and external radioactivity account for most of this destruction.

Hunter and Gradey decided on an illegal experiment. They brought up a small group of children in a strange artificial setting where there was practically no radiation. The setting was improved. The environment grew more shielded as generations passed. At last the Thinkers exploded into a world that had not dreamt of their existence. The world was facing other complications at that moment. An alien had appeared from the other side of the cosmos! Humanity was faced with two potentially deadly enemies; could they be turned against each other, or was one a secret friend?