Doubleday, 1955, 191 pages
Andrew Harlan is an Eternal, a member of the elite of the future. One of the few who live in Eternity, a location outside of place and time, Harlan's job is to create carefully controlled and enacted Reality Changes. These Changes are small, exactingly calculated shifts in the course of history, made for the benefit of humankind.
Though each Change has been made for the greater good, there are also always costs. During one of his assignments, Harlan meets and falls in love with Noÿs Lambert, a woman who lives in real time and space. Then Harlan learns that Noÿs will cease to exist after the next Change, and he risks everything to sneak her into Eternity.
Isaac Asimov was an intellectual author who liked playing with notions of society and history and how science and technology would alter both. He was the quintessential science fiction author for the geeky, pocket-protector-wearing slide-rule-using Man of the Future (nerd) of the 1950s. There's rarely anything messy and human like emotions and character development in his stories; he develops societies and future histories, and his characters are pretty much just placeholders to personalize the events and civilizations he's writing about.
The End of Eternity is a stand-alone novel, not part of his Robots or Foundation series. It has all of Asimov's trademarks -- grand scope and lots of neat sci-fi, and a fixation on the idea of quantifying and engineering human behavior and social evolution. It's also got Asimov's trademark cardboard characters, and makes you question whether he ever kissed a girl. (Yes, I know, he was married and had kids, so presumably he did -- but I wonder if he ever talked to a girl.)
Eternity is an organization of time travelers. They live outside of time and space and take assignments and occupy headquarters that are organized by centuries (which number up into the tens of thousands, but oddly correspond to our dating system; the "875th" century is the 875th century A.D., though 'A.D.' is never used in the book). Eternals are divided into castes by specialty: there are Sociologists, the lowly Maintenance workers, the "ruling class" of Computers, and the Technicians, who only carry out the decisions made by a whole cadre of other specialists but are pariahs because they are the ones who actually execute changes in time which can wipe out millions of personalities and alter entire histories in an instant. Eternity does this for the good of mankind (supposedly); they can calculate whatever historical outcome will result in the net greatest good for the greatest number of people, so they act accordingly, whether it's preventing the development of atomic science or arranging a plane crash to kill a few people and prevent a global war. In other words, they play God with reality and the histories of thousands of timelines.
It's not until about halfway through the book when the morality of Eternity itself is questioned, and it happens through the self-serving motives of a Technician who... falls in love.
I mention above that Asimov's writing did not stand out for its strong characters. This is doubly true of his female characters, who mostly didn't exist. None of the other Grand Master of Science Fiction, such as Robert Heinlein and Arthur C. Clarke, wrote particularly great female characters either, but at least Heinlein's were interesting. For Asimov, women seemed to be these mysterious things that we're irrationally fond of but it's better to keep them away from the gears and moving parts because they'll just cause trouble. In The End of Eternity, the sole female character, Noÿs Lambert, is basically the MacGuffin. Andrew Harlan, who has literally never kissed a girl, becomes completely obsessed with the first one he meets in Eternity (naturally she's totally hot), is immediately seduced by her, and promptly goes about figuring out how to keep her for himself, ignoring years of training and all of his Eternal ethics.
Eternals travel up and down the centuries, from the "primitive" pre-time travel era (ours) to hundreds of thousands of years in the future. Eternals also come from all the centuries Eternals visit, selected according to various criteria. But apparently, not one of these centuries develops a society that produces enough technically and scientifically-minded women to become Eternals. The only time Eternity is mentioned recruiting women is for two purposes: as mistresses/doxies and to do the shit-work of cleaning and cooking. Yes, seriously. There is a mention at one point that for "unknown reasons" it's been found that taking women out of their native time has an impact on history 8 to 10 times greater than taking a man out; i.e., it's more difficult and causes more problems to remove women from their native timeline. Ya see, women just cause problems, whattayagonnado? Asimov obviously had just enough awareness to realize it might seem odd not to have a single woman in the story other than the love interest, but no desire to fix it other than with a stupid hand-waved explanation. Even for the Fifties, this was hardly very imaginative or forward-thinking.
All-boys-treehouse aside, The End of Eternity is pretty good for what it is, a time travel story. The first thing you wonder about with time travel stories is how you handle the obvious paradoxes, especially when it's not just one person skipping through time and trying to avoid trouble, but an entire society that meddles with time on a regular basis. There are only a few ways for an author to handle this (besides ignoring it). You can adopt the "alternate realities" model, whereby when you travel in time, you are actually going to an alternate timeline (or creating a new one if you change anything). This averts paradox but implies an infinity of parallel universes. There is the deterministic universe, which whether by divine agency or "temporal inertia" or some other deux ex machina prevents time travelers from changing things.
No matter what your postulates are, you're gonna have to punt a bit somewhere, because time travel logically cannot exist without paradox. Asimov uses a bit of all of the above. You can change history (drastically) but "temporal inertia" prevents paradox. We later discover that there are also multiple timelines. Asimov uses lots of technical-sounding terms like "physio-time" and "Minimum Necessary Change" and so on, and works out the paradoxes in a reasonably thorough fashion, though of course it's not bullet-proof, as no scenario involving time-travel is airtight if you think about it too hard. It works for the purposes of the story, which is good enough.
So, this sci-fi classic gets an 'A' for its premise and the plot twists at the end in which all the assumptions of the Eternals are challenged. It gets a C for the datedness and hidebound nature of the future society Asimov envisioned, a C for the characters, none of whom we really get to know or care about, and a D for a science fiction author who literally can't imagine women as anything other than conniving seductresses who will destroy everything if allowed into the treehouse.
Verdict: A classic time travel novel, with Asimov's trademark great ideas, plot twists, and cardboard characters. This is a quick, entertaining read with an imaginative premise and a thought-provoking ending, but Asimov's clumsy attempts to handle those mysterious girl-creatures might risk the book meeting with a wall.