Or, 'A Fabulous, Formless Darkness', which was Delany's original preferred title, according to Neil Gaiman (him again?) in his introduction to this edition.
Delany writes twisty puzzle-stories, where it’s not always clear what’s going on, or why. I’m a big fan of his later masterpiece, Dhalgren, which matches that description, for example.
This one is more straightforward by comparison. It is Earth’s far future. Humans have gone, and the world is instead inhabited by an alien race. They have taken over, not just the planet, but humanity’s identity, its myths, even its genetics. And they are struggling to be human.
Or that, at least, is what we are told. That is what our hero, Lo Lobey, believes, what the elders of his village have taught him. But personally, I’m not convinced.
See, there’s nothing here that requires that the characters be aliens; they behave just as humans would, in most cases. Far-future, post-fall humans, yes, but still they could be humans. Sure, Lobey has prehensile toes, there are various other physical differences, and there is a neuter (or hermaphrodite, it’s not clear) ‘third sex’; but none of that is anything that a bit of genetic manipulation - deliberate, accidental, or a combination of the two - couldn’t cause. And there are some psychic abilities, but that is well within humanity’s capabilities in thousands of stories, of course.
More importantly, they feel like humans. As Gaiman says, “they are us.”
There is one element that is more alien, though. That is the curious character of Kid Death, and his (and perhaps some other characters') apparent ability to bring back the dead at will. The latter could be illusion, of course, and would then be in keeping with the psychic powers I mentioned above.
Why does this matter, you might ask? Why do I care whether these people are aliens or advanced-and-fallen humans? In one sense it doesn’t matter, of course. You can enjoy the story while taking the explanation for its background at face value. But there is, to me, something unsatisfying about the “aliens who have taken on the characteristics of humans” explanation. It is too unexplained.
Not that we can or should expect everything to be explained in SF (or not at first, at least); and in Delany’s work this low expectation is perhaps lower than in most. Certainly Dhalgren, for example, gives few clues as to what is going on, or how things have got to where they are (it occurs to me, in fact, that it could be set in the same world as the present story).
To have a story about such an alien race, with no examination of what they were like before they took on the role of humanity, or why they did it, seems a curious choice. But I suppose we could see it as a demonstration of true alienness: there is no explanation of why they behave as they do because we simply could not understand their rationale.
And I think that’s the explanation I like best.