Spoiler level: Medium - High (both for this book and for The 4400: Welcome to Promise City.)
I know I can always expect two things from a David Mack book: a lot of action, and a high body count. After reading his Star Trek: Destiny trilogy, I also knew he had the ability to tie many different plot points together brilliantly. So after tearing through The 4400: Welcome to Promise City, I thought I had a pretty good idea of what to expect from Promises Broken.
I was still a little shaken, however; after Greg Cox's character-rich Welcome to Promise City, David Mack's arc-heavy follow-up feels a little jarring. Especially the radical switch in philosophies between Kyle Baldwin and Jordan Collier. In Welcome to Promise City, Collier is still willing to sacrifice half the world's population to make the other half promicin-positive, while Kyle still believes him to be an honorable man who would never force promicin on anyone. And while this is true on the face of it, Collier is more than willing to sit back and let others do it for him.
However this book picks up "a few months" after the previous book, and right off the bat we see their perspectives have changed; Collier realizes he's headed towards a shooting war with the US government. As a result, he's decided his previous philosophy was wrong, and is now willing to try to live in peace with promicin-negative people. Kyle, on the other hand, has been guided by his promicin alter-ego Cassie into believing war is the only answer. We saw him start to be lead down this dark road in the previous book; he was resistant to it then, but now he's completely embraced it. Each book works just fine, and the two perspectives work fine when you can accept that time has passed between them, but reading them back to back made me feel like there should have been another book in between the two to show us their reversing in philosophies more gradually.
That aside, the book is a non-stop action ride as everything between the US government, The 4400 Movement and the Marked all collide, bringing the entire 4400 series to a satisfying conclusion. And just like the series, it ends raising the stakes with the potential of taking the series to the next level, and opening some new doors if they decide to publish any more books.
Which considering that this book was published in October and nothing new has been announced since then, I don't have a lot of hope of any more books coming at this point... but hope is still there. And if not, if this is truly the ending of the story of The 4400, then it's a good one. Many thanks go out to David Mack, Greg Cox and Pocket Books for making it happen.