The story depicts either a new covenant with God, or a devil's bargain (take your pick) for the human race in which utopia is found in an artificial re-creation of eternal feudal warfare. A world is constructed as though the flat-worlder's were right all along. The brilliant physical description of this world is one of the most mesmerizing elements of the tale. The feudal factions are The Reds and The Blacks, and from these are brought forth the Kings that rule. One faction, The Just, function as a resistance movement, and as the final arbiters of the delicate balance of society. The Grays, equivalent to the clergy, remain aloof. Among these factions walks a sentient non-human being whose function is to record, and to perform certain acts that he has forgotten due to damage he sustained upon his arrival.
On his journey, while damaged, he must think for himself and thus he learns things his maker never intended him to know. What question, what single question does he burn to ask the maker when he returns? We never know, but neither can we forget we must try to remember it.
There are many wonderful twists from the familiar into the alien in this story. Such as transmuting the idea of midwives into Endwives.
I leave you with the words of demi-god-world-keeper Leviathan:
He has sails, and I do not. We are not alike. He is busy and wide-ranging; I am sleepy and stationary. He has sails; sails like woven air, that fine; large as the world. Many of them. They are his speed.
The above may also be taken as a description of what sets John Crowley apart from other writers.