One day alien shops appear in the sky over earth. A race of aliens that are called the Overlords by the humans, tell them they are there to help them end violence etc.. The world because peaceful if stagnant. It is years before the true purpose of the Overlords is known and by then it is too late and humanity is changed forever. 
 this is a sad book. But oen that makes you think and ask questions. And wonder about what makes us human and what our role in the universe is. In this book, it is rather bleak, but one does not need a happy book to be a great one.