I didn't think it was public and then someone said she had pre-ordered it online today! Sure enough, it is out there, so I may as well announce it: Book #4 is called Wild Honey From the Moon. It is a fully illustrated 64 page picture book with seven chapters. It will be released on November 5th, 2019 from Candlewick Press. Here is a summary:
Poor Mother Shrew's little son is sick and the only thing that will cure him is wild honey from the moon. Without hesitation, Mother Shrew heads to the moon, encountering a scheming owl, the wild night mares, and an island of angry bees. It is a perilous journey, but Mother Shrew manages it all with quiet determination and lots of love for her darling young son.