This book was thought-provoking, but also problematic.
In the future, humanity has been reached by aliens and it is now 40 years after first contact. Massive upheaval has rocked all of world, due to the fact that the 3 alien races that now interact with mankind also cannot in any way communicate with us! They're just too alien! They don't communicate using sounds, have no oral or written language, one of the species doesn't seem to be made up of cells per se, one seems to possess rudimentary telepathy (which humans can't join in), and the third lives in a symbiotic/mutualistic relationship between a large grub-like creature and a dog/deer quadruped that provides the grubs with locomotion. What all three races have in common is their desire to trade with humans, but the trades are . . . bizarre. The aliens show no interest in classical human art, science, religion, politics, or philosophy, but are willing to swap enormously advanced equipment (but not the technology behind the equipment) for things such as a rusted bicycle, a dinner place-setting (dinner included in the trade), a single, well-worn tennis shoe, or certain artistically designed mobiles that are interrelated in that they contain actual Earth lifeforms within them (protozoans, fungi, jellyfish, etc.).
So weird!
All national/international governments have fallen, and people live more in city-states and large fiefdoms rather than massive nations. Since the aliens won't recognize or deal with politicians or governments (or religious leaders, or scientists), people have decided they don't need to either. Now you live with and pledge loyalty to your clan of people who live near you and speak the same language you do!
Human-researched scientific discoveries have dropped to nearly zero, as deciphering and/or reverse engineering alien devices now consumes all scientific endeavor. (As the author puts it, "Why invest billions of dollars and decades of research on a discovery some alien may simply TRADE with you tomorrow for an old oaken door?" Because of this, human science -- and, to an extent, human advancement -- has begun to stagnate.
Then one alien race kidnaps a group of human religious pilgrims, whisks them off to a nearby Earth-like world, films them (the aliens) assassinating two of the pilgrims, and then sends a video-recording of the event to a human artist whose work they've traded in before. Is this a message? Are they trying to communicate at last? Are they unhappy with the last trade with the artist? Do they want to trade MORE with the artist? Is this a warning to all humanity? What does it MEAN?
Who knows, but mankind decides it must put together a rescue mission for those pilgrims still held by the aliens, and so the story begins!
Like I said, a thought-provoking work, to be sure.
What's problematic is that in order to make the aliens uncommunicative, ALL communication must fail, and it does. What, the aliens don't use fire, electricity, radio waves, or mathematics? All three of them? Well, it seems that they don't! Really? Then how did _they_ create all the technological shit that they trade?
Whenever a possible explanation is put forth, you're never really sure if it's correct or not. But once the characters in the tale exhaust their answers/interpretations, well that's that -- the narrative has to continue, so you'll just have to either accept their resolution (or not) because the tale is going onward.
Another problem is the one brought up by Arthur C. Clarke in 1973: "Any sufficiently advanced technology is indistinguishable from magic," and this book has that in spades! In several situations alien technologies appear like Holy Grails/MacGuffins to bail out the humans from situations they're in, and this makes for some unsatisfactory extensions and endings to some subplots.
The whole psi/psionic power subplot toward the end is grandiose and unnerving. Read it and see.
But I enjoyed this read because it made me think, and offered a plausible, explained, well-reasoned, and totally bizarre future for humanity. It was _original_! Something new under the sun!
Not many SF books can claim that these days.
That's why I'm giving this one 4 stars despite its flaws.