Andrew Harlan is an Eternal, a man who has been extracted from ordinary Time to live in Eternity. The Eternals are an elite, lonely bunch, dedicated to an almost monastic life outside of Time, committed to policing humanity by making Changes--usually very small ones, such as a book set on a different shelf or a burned out lightbulb replaced--that will, nonetheless, prevent dangerous or risky developments from occurring. The Eternals have reversed more than one Reality close to developing nuclear weaponry, for example. Eternity is, to say the least, a paternalistic institution. Harlan is a Technician, the person responsible for implementing Changes; he travels, as all Eternals do, up and down the Centuries, never belonging to any one era, never making any real connections, certainly never falling in love.
Until, that is, he does. And when that happens, Andrew Harlan will do whatever it takes to be with his love, whatever the cost to the ages.
The End of Eternity, as so much of Isaac Asimov's greatest work, is set against a backdrop that spans millennia, hundreds of millennia, even. Unlike many of those other works, The End of Eternity is rooted firmly on the earth. There are no spaceships, no other worlds, no galaxies, and yet the universe he portrays is as vast as that of the Foundation Trilogy.
Isaac Asimov is not known for either his writing, which is pared down and basic, or his characters, which are frequently cartoonishly broad. But these deficiencies are more than made up for by the vastness and brilliance of his imagination. Asimov's science fiction, like much of that of the Golden Age, is one of ideas, big ideas, and The End of Eternity is no exception. How safe can man keep himself? How safe should he keep himself? Should man's reach exceed his grasp? What would be the result if the spirit of exploration and risk-taking that characterizes our problematic species were extinguished every time it showed evidence of itself? Asimov answers these questions admirably, and in doing so sets his fictional universe up for the coming of the Foundation, a neat little twist at the end of this grand stand alone work.