I would echo bgibson's comments. The first two Atlee Pine books were good. This third one, still on the search for twin Mercy, is cluttered with a unbelievable plot. The search for Mercy seems to have gotten lost in the process.
Recommend "cheating" and going to near the end of the book where it goes back to the search for Mercy and provides a pretty good summary.
I found this third book not worth the trouble to read and a big disappointment.