Arthur's lost library book

Arthur was the first to take out the "Scare Your Pants Off" book from the library. A week later he can't find it. Something's weird. It couldn't have just walked off, or could it? ALSO... Someone only D.W. can see has moved in with the Reads. Ner name is Nadine and she follows DW everywhere. Arthur is upset because he is embarrassed in front of all of his friends.