It's fascinating to see how some sf novels stand the test of time and others don't. I still have my old Mayflower pb of "The Long Tomorrow" which I purchased as a teenager c1963, and reread it from time to time. Doing so produces most curious feelings, like going through a timewarp of some kind.
TLT is a "Golden Oldie". Published in 1955, it is one of the huge number of "post nuclear war" stories that came out in that nervous era, but is head and shoulders above the bulk of them. It's theme, unique in sf as far as I know, is a future world in which the Amish (or at least a sect more or less "cloned" from them) have taken over America.
The idea that, in the aftermath of holocaust, the people might turn against science and technology, has of course been used by others, notably Walter M Miller in "A Canticle For Leibowitz". But TLT takes a subtly different angle. The New Mennonites are not opposed to education, their children are literate, and they seem to live at an early 19th century level, just pre-railroad. It isn't a Dark Age in the usual sense. But there are strict limits. No electricity, industry or anything high tech. Riverboats are allowed to have simple engines, but land transport stops at the horse and buggy. Above all, the US Constitution has been amended to forbid the existence of any city or town above 2000 people.
The central characters are two teenage boys in a New Mennonite community in Ohio. Len Colter (14) and his slightly older cousin, Esau. They discover a radio set, belonging to a passing trader, and realise that he comes from "Bartorstown", a secret society out west conspiring to bring back the bad old days, association - real or alleged - with which can result in whipping at best, instant lynching at worst. Fascinated by it (and, in Len's case, by their grandmother's wistful recollections of before the war) they seek to know more. This leads to their having to flee from home, and set out on a quest to get to Bartorstown. This quest covers several years and forms the middle third or so of the book.
On arrival, they are in for a mighty shock. These people are the custodians of the last surviving nuclear reactor, and are seeking a way to neutralise atomic bombs, so the power of the atom can be safely used without another catastrophe. This forces the sensitive Len (by now more or less adult) into a crisis of conscience. Is this a wise path to take, or were his elders right all along? The last part of the book is about him coming to terms with this question.
Perhaps my strongest reaction, on going back to it, is surprise at finding the Amish (on whom the New Mennonites are explicitly modelled) cast as the Bad Guys. This, I suspect, would be out of the question today. If their treatment by Hollywood ("Witness", "Harvest of Fire" etc) is anything to go by, they are about the most popular ethnic minority in America. To chide them for holding up "progress" would be almost unthinkable.
The book shows its age in other ways too, notably its simple 1950s faith in technology. It's now some 80 years since World War III, yet the group at Bartorstown are perfectly happy living next to a prewar nuclear reactor. Even those who for various reasons aren't happy with it don't seem to fear any physical danger, save of course from the neighbours if they ever find out. These days, I suspect few would be keen to live even near an eight year old one. Yet Bartorstown has lasted three generations without even a Three Mile Island, let alone a Chernobyl. Remarkable workmanship.
Even the nuclear war itself seems to have left remarkably little damage in its wake, with no deformed babies, no cancer, etc, while Len's grandmother, who experienced the war as a child, has lived to a ripe old age. The only lasting harm seems to have been psychological. Nor does anyone see a problem about restoring civilisation in a world where the oilfields are probably mostly drained. It is just assumed that such things can be got round. This is the outlook of a different era from today.
Ditto for the people. There are some who'd rather not be living there, but after eight decades in a country hostile to all it stands for, Bartorstown still hasn't been betrayed or detected. Could anyone really keep the lid on for so long? Quibble, quibble, Mike.
In short, TLT is a remarkable glimpse into "The way the future was" as of 50 years ago. If it were written today, I suspect the Mennonites would be definitely the guys in white hats, and the young heroes would not merely get out of Bartorstown, but do their best not to travel downwind of it any more than they absolutely had to. This said, however, it is beautifully written, and one of the best books of its kind. Read it as an sf "period piece" and you won't be sorry.