The End of Eternity

Harlan is given an unusual assignment: to teach a young man, Brinsley Cooper, about the distant past, in preparation for a mission that only a few senior Eternals understand. At the same time, on a visit to a far-future century, Harlan meets Noÿs Lambent, a beautiful and mysterious woman, and falls in love with her. When he learns that a Reality Change will erase the life she knows, he breaks the rules of Eternity to save her.

What follows is a puzzle of loops and paradoxes in which Harlan begins to question the whole purpose of Eternity: whether a humanity protected from every risk can still reach the stars. Asimov writes in a clear, brisk style, and much of the book consists of ideas and conversations rather than action. The romance is a little old-fashioned, but the time-travel logic is carefully worked out and the final revelations are memorable.

Smart, inventive and surprisingly romantic, a standalone novel admired by many readers as one of Asimov's best. It works well for anyone who loves time-travel stories that take their rules seriously. About 255 pages in the Orb paperback.