In a series of letters a student laments the absence of her teacher and daily routine, but she soon realizes there are benefits to mixing things up, and that perhaps having a substitue teacher is not so bad afterall.

"Milton Worthy can't wait for his class trip to the city zoo. But little does he know that Noah--part time classroom pet ferret, part time evil mastermind--has escaped and stowed away on his school bus. Good thing that Mrs. Worthy, ace world-saving, member of the super-secret Society of Substitutes, is along for the ride! Will Milton and his super-substitute mom be able to stop the zoo from running completely wild?" -- Page [4] of cover.