Because this book is so closely connected to its predecessors, I would not recommend reading it until the previous three--and possibly the companion novels of Masters and Slayers by the same author--have been read. Even though I had read the books before, it had been a while, and I had difficulty remembering some points.
As the stakes grow higher, everyone has difficult choices to make. Multiple heroes, all with one goal--freedom for the slaves of Darksphere--must chose what path to follow to that goal.
One aspect of this book I admire is how complex the characters are. While many fantasy novels have simple heroes and leave the complex motivations for the villains, Davis manages to create believable, honorable characters who wish to do the right thing, but are uncertain which path to take. Koren and Cassabrie are especially strong examples of this trait, leaving the reader guessing.