Against the Fall of Night Author:Arthur Clarke Destiny in the hands of a boy - A terrifying choice faced the boy, Alvin. For millions of years his people had remained content behind the barrier of the wasteland, obeying the warning of the records: Leave the city and the Invaders will return from beyond the stars...bringing ultimate doom. Hidden behind the records was another truth - and the ... more »boy sensed it. The long slow peace was a long slow death for his race unless he, Alvin, could accept the awful challenge. Abandoning the safety of Diasper, Alvin made his choice - embarking on a voyage that gambled the fate of all mankind against all eternity.« less
This is a very famous book, one of Clarke's earliest. He entirely rewrote it and republished it as "The City and the Stars" but many consider the first version as the best one.