We left Ash under siege in Dijon with people starving as well as dying from attacks by the Carthaginians. In this book, her sister Faris surrenders to them, but the King-Caliph from Carthage comes to fight with more warriors and some of the leaders Faris has conquered. Ash needs to find a way to keep the Duchess of Burgundy safe, but it doesn't look like she can. If she can't, the Wild Machines will destroy the world. What can she do?
This gives a satisfying ending to the series, and the interleaved pieces plus an afterword from the author-character give a firm SF base to the entire set. I really liked this series and highly recommend it.