Anathem is a novel by Neal Stephenson.
It is almost impossible to summarize Anathem — it’s 930 pages, plus an extensive glossary, three appendices, and a web page full of acknowledgments and sources. So, what can I say about the novel?
I think Anathem is a great novel, but you may hate it.
It’s a novel of ideas — very intensely so. It’s science fiction, and it’s a variant of a particular genre of science fiction called alternate history. But usually, in alternate history, a particular event is changed, and the author guesses as to how history would change — the South wins the Civil war, Adolf Hitler is stillborn, that sort of thing. You can recognize the names of people and places. In Anathem, this is not the case — although a lot of the characters are analogues of ancient Greeks. You can see Pythagoras, Socrates, Plato and others, but not by those names, and there is no place called Greece.
Anathem in fact, is almost an alternate history of philosophy novel.
One way to look at it, one that the author might have been playing with, is, “Suppose that the ‘dark ages’ came immediately after the classical Greek period” because, while there are analogues of the ancient Greeks, there are none of the Romans, and none of the Romans; there’s no Jesus or Mohammed.
In Anathem there are monasteries, called ‘maths’, that are quite similar to what we think of as monasteries — but the residents called ‘avout’ are not religious monks as we would think of them, they are mathematicians and philosophers. There’s a long history to the planet “Arbre”, detailed a bit in a chronology at the beginning of the book, including several ‘sacks’ where the secular power attacks the maths..
Of course, even a Neal Stephenson novel can’t be just about ideas — there are characters and there is a plot. The protagonist is Fraa Erasmus — a young avout. During the course of the novel he falls in love, becomes a hero, loses some friends, makes some other friends, and grows up a lot. The plot is complex, and I won’t spoil the novel for you by detailing it. But a writer of Stephenson’s skill could tell this tale in many fewer pages. What he seems most into is the ideas behind the world, and the re-creation of the alternate history. As Anathem unfolds, he also shows interest in what constraints nature might place on the nature of intelligent beings.
If all of the above sounds like your cup of tea, then you will probably love Anathem. If not, not. I don’t imagine many people will feel neutral about it.