Katie Carew is so excited for the weekend! She has big plans to attend Suzanne's amazing all-girl sleepover party. But her friend Jeremy has a completely different idea. He wants Katie to go with him to ride the terrifying new roller coaster at the amusement park instead. When Katie chooses the party, Jeremy gets annoyed. In fact, he and the other boys in Class 3A decide that all girls suddenly have cooties! The classroom turns into a giant battle between the boys and the girls. But then, the magical switch wind blows, and Katie actually finds herself stuck in Jeremy's shoes. Now that she is a boy, Katie has the perfect chance to fix things and reunite the class. Can she figure out a clever plan to end the cootie war before it turns into one massive mess?