Spring has come to Munchem Academy. The snow is melting, the roof is leaking, and Mr. Larimore is now in charge. Mattie is worried, though. Mr. Larimore is taking the whole "let's help Headmaster Rooney get back on his feet" thing seriously, and he's whispering all sorts of suggestions to the highly suggestible Rooney.

Then there's the matter of the school's weather. It's getting . . . strange. Mini-tornados sweep up out of nowhere. Rain pours inside. And there was that snowstorm-that yellow snowstorm-that lasted for two days.

Once Mattie, Caroline, and Eliot figure out what's causing the chaos (the Weather-matic 9000), who's causing the chaos (Mr. Larimore), and why it's a chaotic an idea (weather weapons!), they need to act. Fast.

There's only one thing to do: save Mr. Larimore-and the world-from Mr. Larimore. It's a tall order for a short kid, but Mattie has a plan. After all, what's a little breaking and entering among friends?