Walter Jon Williams is one of my favorite authors. His novels share two broad characteristics. First, they are fantastically inventive -- Williams doesn't like to stick to one genre, and has written cyberpunk, a SF police procedural, alien contact novels, space opera, high farce, and more genres than I can name. Second, no matter what the genre, Williams' works typically incorporate a physicality that is missing from most SF. A martial artist himself, Williams is at his strongest writing about the ronin of the future, and, with various variations, usually does exactly that.
Implied Spaces is a mix of fantasy and sf that reminds me a little of Heinlein's
Glory Road or Zelazny's
Chronicles of Amber, with a higher-tech background and the plotline of Williams' high nanotech novel,
Aristoi.
The novel is set in the far future, where humans have become effectively immortal and generally live in artificial and tailored universes created by the humans and their AI. The protagonist, Aristide, is another one of Williams' ronin characters, a man who has outlived his original sense of purpose and is essentially drifting. Together with a magic sword and a talking cat (both of which are scientifically explained, of course), Aristide wanders the various universes, studying the "implied spaces" -- areas of the world which were not intentionally created, but arose by implication.
While studying these unintentional areas, Aristide comes across a universe-spanning threat, which kicks off a plot too idea-packed and fast moving to really summarize. He ends up on a very fast paced quest that uses Williams' original premise to dip into new genres every chapter - zombie movies, war movies, existential novels, philosphy about the nature of identity, and a quick moving conspiracy thiller.
This book has enough clever ideas to fill four or five novels, and is well worth reading. Still, I can't say that it's Williams best work. First, there are so many ideas that it often feels like none of them is getting enough screen time -- this might have been better as a multi-book series. Second, while not identical, the plot is disconcertingly similar to an earlier (and IMHO better) Williams novel, Aristoi. Williams is a daring and experimental writer, and it wouldn't surprise me that he *deliberately* set out to write a variation on a previous book, but as a reader, I found it disconcerting.
All in all, I would recommend this book to any sf or fantasy reader, and especially to fans of Williams, but it's not the Williams book I would start a new reader with. IMHO, new readers should look at
Voice of the Whirlwind,
Aristoi, or the
Metropolitan/
City on Fire series, which I think show Williams at his absolute best.