The End of Eternity

Humanity has found the ultimate way to fix its own mistakes, make them never happen. In this book, a group of men that lives outside of time, the "Eternals", modify time. Harlan Andrews, a low ranking technician, is loyal to the idea that unites all Eternals: it is better to change time to help the many, even if it means hurting the few. That is, until he learns that the woman he has fallen in love with, Noys, will be eliminated in a soon to occur time change. So, violating the principals he had always held to as an Eternal, Harlan saves his lover. But soon, he finds that he is part of a much larger conspiracy.