Another stand-alone (well, mostly) book that is separate from the main story line of the series. In this one, we catch up with Belinda Lawson (last seen in book #3), and we move to one of the Core Worlds, to see what's happening after the Fall of Earth.
A lot less military & political than the rest of the series. Instead, this one is a mystery of sorts, with the two protagonists racing against the clock to prevent a major disaster.
As I read it, I had a pretty good idea where the danger was going to come from, although not the exact nature of the threat. (Yes, that's vague but I'm trying to avoid spoilers.) And I'll admit that for a couple of bright individuals, the two people at the center of the story didn't exactly think through all the possible implications of what they'd seen. Then again, it made the story better.