** spoiler alert ** I can remember reading this decades ago and thinking it was the least satisfying of the Asimov novels I'd encountered so far. (This was a long while before he re-entry into the field with the gasbaggy recursions.) For about the first half of this new reading I was thinking much the same -- in part because it took me a while to adjust to Asimov's flat, deliberately unflowery (I'm tempted to say deflowered!) style. The characters seemed to be comic-book stereotypes, with unsubtle, adolescent reactions and motivations. I was concerned, too, that there seemed to have been almost zero physical or even cultural evolution over periods of millions of years.

But, now that I've finished the book, I realize that a lot of this was deliberate on Asimov's part: he was trying to present a society in which people had become that way because of (a) their constant exercise, however benign the intent, of the power of life and death over billions and (b) a long, self-imposed cultural isolation from others not of their kind -- even including, because this society is almost exclusively male, an isolation from women. This isolation despite the fact that the society's denizens are viewing and on occasion interacting with all human cultures over a period of no fewer than 70,000 centuries.

I'm kind of getting ahead of myself.

Eternity is a sort of timeless but dimensional structure created to exist alongside Time (the capital T is deliberate). It's possible to travel "upward" and "downward" in Eternity, as if by elevator, from the time of its creation in the 27th century to the very far future, stopping off along the way to view or enter Time. The people who live within Eternity have as their task the regulation of trade between different periods and the monitoring of Time to ensure that, always, all will work out for the best for humanity in the best of all possible worlds. They do this by giving Time's reality occasional -- or not so occasional -- tweaks, these manipulations bringing into being new and supposedly preferable realities, whose substitution for the status quo ante will do good in the relatively short term and won't in the longer term adversely affect the triumphant story of humankind.

As a Technician, one of the castes in the rigidly stratified society of Eternity, Andrew Harlan is one of those whose task it is to effect such Minimum Necessary Changes (MNCs) -- and he's an expert at it. One day he's virtually thrown by his superiors at Noys, a beautiful aristocrat from the 482nd century, when fashions in female clothing were conveniently scanty. Soon, despite Andrew's determined Man-of-Steel persona, they become lovers -- in case it's an obsessive love, one that barely flickers when it's broken to him that there's a superstition rife in Noys' time that women can become immortal through boffing Eternity employees. (Now, I wonder who could have started that rumour?) The liaison is in a legal grey area; but when Andrew discovers the next MNC in the 482nd century will eliminate Noys's existence entirely, he starts breaking every law in Eternity's books.

Adventures ensue.

In the final stages of the book we find that Andrew has been thoroughly manipulated -- not simply, as he himself elicits, by those in the Eternity hierarchy who're using him to help set up the closed time loop that is necessary if the creation of Eternity is to have been effected in the past, but more complexly by the inhabitants of the very, very far future, who have realized the existence of Eternity will eventually doom our species and have sent back Noys to engineer, through manipulation of numerous others as well as Andrew, a situation where Eternity has never been invented:

Any system like Eternity, which allows men to choose their own future, will end by choosing safety and mediocrity, and in such a Reality the stars are out of reach. (p180)

This is a point subtly different from, and very much more interesting than, the usual free-will speculations and philosophizing I'd been expecting -- although there are some of these as well. In this light, we have to recast our ideas of what all of the earlier text was actually about -- as indicated above, suddenly so many things that had seemed like defects or clumsinesses are instead revealed as yet another piece of manipulation, this time of the reader by the author! It's a wonderful piece of volte-facery.