In this twentieth Henry Heckelbeck adventure, Henry uses his spy skills to go undercover!Henry Heckelbeck's spy senses kick into full gear when he sees his school principal lurking inside a bookstore. It's odd enough to run into your principal outside of school, but when he's also acting suspiciously, Henry knows he has to get to the bottom of it and crack the case. And he's going to need a disguise or two to figure it out! With easy-to-read language and illustrations on almost every page, the Henry Heckelbeck chapter books are perfect for beginning readers.