I'm currently working on chapter 20 of Perilous Waif, so the end is finally in sight. I'm currently projecting that this book will be 27 chapter long, so by next month I should have a good idea of when it's going to be finished.
The audiobook version of Extermination is now available on Amazon. I expect that future audiobooks will be out within a month or two of the e-book version, since that seems to be how long production takes.
For those of you waiting for the next Daniel Back novel, I plan to go back to work on it as soon as the first draft of Perilous Waif is finished.