I’ve received a great deal of feedback on the ending of Vital Deception. For those of you who haven’t gotten to Book Four yet, without giving it away, I can reveal that the last paragraph of the book proposes a question. Some readers have called it a “cliffhanger,” and it sort of is just that, even in a loosely literal sense.

I can also reveal (confess?) that when I completed the manuscript and published the book, I didn’t know the answer to that question. But, really, the answer is not at all im...