My name is Zosia and I carry a rucksack from my uncle Teo. It's a bit tattered, but it has lots of weird pockets. On Monday morning, I found a metal shackle inside. It was as thin as a ruler and next to it was written: WEATHER. I thought it was a joke, probably another inventor's toy. I snapped it on for a test, just as I was walking in front of the school. The sky blinked like a TV after a storm and the leaves trembled. A breeze gushed from my back pocket, cool as ice. My hair stood up and Leon burst into laughter. He said: "Sophie, I think you've turned on hairdresser mode." I shifted the control knob from the HAPPY position to SLOW. The wind had died down, but there was something burbling in the backpack, like a washing machine with a block. The bell rang, so we ran into class 4B. The maths lady started the lesson and I glanced at my backpack. The switch vibrated again and I clicked on the LIGHT DESK option. Drops appeared on my bench, big and shiny. Leon stuck out his tongue and said they tasted like compote. Several children pulled out their cocoa cups. The maths lady looked up from under her glasses, as if she were counting clouds. She said: "Whose clouds are these?". Then tiny cumulus clouds, white as chalk, began to rise from the ceiling. One cloud sneezed on the blackboard and clashed the task. I shifted the switch desperately to SOUTH IN HOLIDAY. The clouds obeyed, but in the corner of the room something buzzed. A new scale slipped out of my backpack: STORM, GRADES, NECESSARY, CONCERT OF GROMBS. My finger twitched of its own accord, as if someone had tickled it. The door to the classroom opened creakily and very slowly. In the threshold stood the headmaster in his new suit. All the clouds looked up at him, and my watcher stopped between STUNNING and UNSTOPPING. We heard the first, very quiet but promising crackle.