"Matilda promises her little sister Clemmie an amazing weekend spent playing outside. But the weather's rainy and Clemmie can't bring her new balloon along. Matilda teaches Clemmie all the delights of a wet Saturday"-- Matilda promises her little sister, Clemmie, an amazing weekend spent playing outside. But the weather's rainy and Clemmie doesn't want to go outside. Matilda teaches Clemmie all the delights of a wet Saturday.