The Consuming Fire
The Consuming Fire is the sequel to The Collapsing Empire. If you liked that, you'll like this. I did, and I did. My reservations: there's really not enough description of people, places, and events; the villains aren't especially competent; and the final resolution seems like something that the protagonist really should have done around chapter four. There's couple of nice bits in the middle about how people interpret other people's intentions through their own lenses, though.
Like the first book, this is not a must-read instant classic. It's good workmanlike old-school SF, with John Scalzi's typical strengths and weaknesses. Start with the first book.