Publisher's blurb: Josh and Jenny's school is suddenly overrun with substitute teachers. But these aren't the usual substitutes. These substitutes all look alike, ask a lot of questions, and record everything the students say. Luckily, Josh and Jenny still have their teacher. Until one afternoon they return from lunch to find their teacher missing, and a substitute in his place. What happened to Mr. Ott? Josh and Jenny decide to find out for themselves what is going on in their school. What will they find, and will they save their school? The ending is Up2U. Aligned to Common Core Standards and correlated to state standards.