Childhood's End by Sir Arthur C. Clarke
When the silent spacecraft arrived and took the light from the world, no one knew what to expect. But, although the Overlords kept themselves hidden from man, they had come to unite a warring world and to offer an end to poverty and crime. When they finally showed themselves it was a shock, but one that humankind could now cope with, and an era of peace, prosperity and endless leisure began. But the children of this utopia dream strange dreams of distant suns and alien planets, and begin to evolve into something incomprehensible to their parents, and soon they will be ready to join the Overmind... and, in a grand and thrilling metaphysical climax, leave the Earth behind.