Like any sensible freelance children's book writer with a cat, I emailed my editor and told her my vet wanted to know if there was going to be a fourth moon book.
My editor emailed back say say she intended to discuss that very possibility with the appropriate person to discuss those kinds of things at Houghton Mifflin Harcourt.
The next day, my editor emailed me to say she had indeed discussed the possibility with the appropriate person and she and the appropriate person were interested in the idea. They particularly liked the concept of setting it a number of years later, so any babies or potential babies from This World We Live In would be teenagers. She suggested as an alternative possibility setting it 3 or 4 years after This World,perhaps focusing on Jon, but I don't like that concept as much.
So nothing is definite, but the next step is mine to take, which is to come up with something resembling a plot. I intend to finish polishing The Offering (previously known as Hart) first, and that's going to take a few more days. Then I'll let my brain focus on possible storylines for The Shade Of The Moon, and when I'm satisfied with what I come up with, I'll write it down, email it out, and see what happens.
No matter what, I'll be sure to tell you and my vet!