Zahn is normally pretty good at hard SF. His plots normally rely on strange, even bizarre, turns of science, but they're usually relatively believable and internally consistent. He also has a very good tendency to "play fair", in that when he gives a character a powerful ability, he puts in some weird compensating weakness to limit the effective power. Unforunately in this book, he doesn't manage to do these things very well.
This is a tale of aliens among us, and unfortunately, the aliens are cavalierly granted powers that defy the laws of physics without any real explanation. It's hard to maintain a suspension of disbelief while reading the book, and hopeless once you sit down and think about it afterwards. The author also has a tendency to abuse his position, in that he more than once gives the reader enough information about something that the reader is primed and ready to learn something, only to snatch the revelation away at the last moment, as if he's teasing a kitten. It's not all bad -- there's a lot of fast paced action, and there's also some character development and insight into understanding people who think differently. Really, Zahn is a good enough writer that it's fairly entertaining to read; it only really falls apart once one starts to think about the story critically afterwards. But at that point, it falls apart in many ways. It occurs to me that perhaps the stuff that falls apart so completely is meant to be allegory, and there is some underlying message that we could take home -- but if it's meant to be allegory, Zahn should not have chosen such a realistic present day setting.
Not horrible, not actually bad, but not good either, which is disappointing from an author who usually delivers better. 5 out of 10.