Monster In The Dark (Book 2 of "The Mustela Secret Service")

The farmhouse was very quiet. The ferrets’ Human pets had all gone to visit their Cousins for Christmas. Only Dad Human’s friend, Harvey Man, would be coming by to feed them and play with them.
Suddenly they saw a horrible, ugly face in the window! It was a monster! And it wanted into their house!
Goliath had never been so scared in his life.
Nova had said that he was the biggest, strongest, bravest ferret ever to live on the farm. He wanted to be brave! But when even their smartest ferret was scared half to death, how could he protect his family from this horrible monster, and keep them safe until the Humans came home again?