Kathy Addams and Freddie Fung are two typical, fourth graders at Morrisville Elementary School. That is until they put on their Junior Safety Patrol sashes and the school bell rings, which is when their wild imaginations instantly transform them into Katty Kat and Foo Foo Fat, Protectors of the Playground! Their never-ending quest to defeat their arch-nemeses Doggie Hat and ArmPit from their evil plans becomes even more challenging when the Queen's Traveling Diamond Exhibit is stolen from the City Museum, a new foreign exchange student comes to Morrisville Elementary School, and the Russian Traveling Circus comes to town. Can Katty Kat and Foo Foo Fat solve the mystery of the missing diamonds before it's too late? Will Kathy and Freddie be able to elude Principal Higgins' watchful eyes long enough to find out? And how is the mysterious new student, Alexa Krumpet, tied into all this? Only Katty Kat and Foo Foo Fat can find out, save the day...and keep the playground safe for all Humanity!