I would like to apologize for posting the same Mean Monkey Monday cover twice. To show you how sorry I am, here's a book cover depicting "20-foot-tall telepathic, teleporting beavers [that] terrorize mankind."
(Spoiler) Here's the last page:
"The third possibility," said Brogan. "The machine has undone the effects of the radiation. He is no longer a genius. He is a normal nine year old again."
"Sinclair," said Barney. "I've been thinking. I believe he did it on purpose. He wanted to be normal again. He did what he had to do."
"Now then!" exclaimed Brogan. "That must be it." He stroked his great beard thoughtfully. "The boy built the machine for us, saved humanity from the menace of the radio-active beavers, then decided that he didn't want to be alone on his pedestal of super genius."
"He must have known," broke in Sinclair, "that the machine would neutralise the strange brain powers which the radio-activity had produced. I'm not really sorry though, it would have been a horrible thought to realize that there was a nine-year old child walking around with a brain powerful enough to destroy the universe."
John Holbo asks, "Should the boy have 'gone Galt' instead?"
