Debbie Macomber’s “A Mrs. Miracle Christmas” is a charming tale for the holidays. It centers on the McCullough family, who are eager to have a child. Mrs. Miracle shows up when they need assistance taking care of their grandmother Helen. Her presence is joyful and full of enigmatic clues that point to the impending delivery of a unique baby. The Christmas joy and the wonder of life are encapsulated in the book.