Though this also end at an odd point in the overall narrative. SPOILER ALERT ON REMAINING PORTION OF THE REVIEW!
I expected the end of the third book to be Jay, Kate, and the kids arrival (or at least those surviving that far) at Mac's refuge, but that is not the case. So, now I expect that will be the resolution of book 4. Which would then lead to the question of what could book 5 be about, so it is possible that book 4 will not end at that natural seeming point of reunion--which would then come at the end of book 5. But that seems to be an awfully long stretch for the story arc to me, at this point.