Substitute Trouble (Nikki & Deja, Bk. 6)

Deja is dismayed to learn that her teacher has had an accident and a substitute will be taking her place. Under the new sub's care, nothing is the same in Room Ten. A few of the class troublemakers plot to take advantage of the clueless teacher, and soon other students join in. Should Nikki and Deja go along with the rest of the kids in tormenting him? Should they help him out by tattling on their classmates? Or is there another way to handle the situation?