Best last line, ever. I had to get that out first; it’s an important observation because the last line of this book perfectly illustrates the cyclical nature of the trilogy. The line serves as an explanation (even without the benefit of the epilogue), a conclusion and a beginning. The story is far from over, though the Dire Earth Cycle is definitely complete.
That is a rare thing in speculative fiction; to come upon a satisfactory conclusion. More usually, an end is simply a pause, a chance for the author and reader to take a breath before they launch into the next trilogy. No doubt, this is a pause, too. But the next chapter in this saga will be very different. James M. Hough will not return to tell the same story from a different point of view.
On to the book, itself. The Plague Forge is the last volume in the Dire Earth Cycle and everything is wheeling toward conclusion. The timetable is compressed, again, the window between visits from the Builders the smallest yet, and there seems more to do. Three keys are still to be found, mysteries unraveled and villains dealt with. No one pauses for breath, least of all the reader as the pages seemingly turn themselves.