It's a sci-fi mystery and I had the big secret figured out by about halfway through. Not that that's a bad thing, but the characters should have figured it out by now, too, because it's not a huge leap of the imagination, and certain connections would probably be much more obvious in person.
Also, it's science fiction set at least six thousand years in the future, except that it's mostly set in about 1990.
But it's the physics puzzle that's really bugging me. Okay, so they have flying cars, right? They way they work is they have antigravity pods that create an envelope around the vehicle that cancels 9/10 (standard setting) of the its weight, making it easy to fly around with minimal thrust and lift. "The envelope is no larger than necessary to ensure that the entire aircraft, wings, tail assembly, whatever, is enclosed. If you could see it, it would resemble a tube."
So the protagonists take off to fly somewhere and discover that the control cables to the antigravity pods on their vehicle have been disconnected and the pods set to 100%. Oh no! They start to ascend uncontrollably, and are going to suffocate and/or freeze to death in the stratosphere in fairly short order.
(I'll pause here if you want to think about it.)
Now, it seems to me that there's a pretty obvious solution to this problem. The reason they're rising is that everything inside the antigravity envelope weighs less than the surrounding air (i.e., nothing) and so buoyancy is pushing them upward. All they have to do is dangle something vaguely heavy outside the envelope and it will drag them back downward. It doesn't even have to be all that heavy. Assuming the vehicle is about the size of a car, that's what, 2 meters by 2 meters by 5 meters? Be generous and call it 30 cubic meters for the volume of the envelope. At sea level, that'd be 36 kg, or about 80 pounds. At 4 kilometers altitude (mentioned in the book) it's only a little more than half that. A pretty straightforward fix, not that hard to pull off.
But that's not what they do. Instead, they have one of the characters climb outside the vehicle, dangling within the zero-g envelope by a makeshift tether, to reconnect one of the control cables from underneath the skimmer. (The other pod is inaccessible, so they have to dangle nose-down as they drift downward and ditch in the ocean.) And yeah, it's dramatic, and kind of cleverly counterintuitive, but it just seems way too complex and risky (and time-consuming!) when there's a much simpler solution.
I would even have bought it if someone had suggested the simple solution and then discarded it as unworkable for one reason or another, but I think the author just didn't bother to think it through. Isn't that the whole point of science fiction, to think through the implications?