It's the final book Each of the Eights has received her power and gift and they even know where Daddy is--inside a snowglobe-shaped Christmas tree ornament. Now all they have to do is get inside the ornament and rescue Daddy. Hopefully, Mommy's in there with him.
For heaven's sake, how are they supposed to shrink all of them (plus the cats ) down to a size small enough to fit in the globe and then actually get inside it? Of course, through magic or just shear will power--who really knows which--the girls have done quite a few things that, to be honest, they really shouldn't have been able to do. But this seems like asking too much even for these intelligent and talented girls.
But the Eights are also a very determined group. Now that they know where Daddy is, they will--and they do--find a way to him. But they never would have guessed what else awaits them inside the snowglobe.