Up, up and away - Nancy Holder

Sabrina, Harvey, Valerie and Libby have one week to redo their pathetic science project about space. But before they have a chance to begin, Sabrina finds a puzzle with a spell that transports them to Paris in 1783. Suddenly Sabrina and the three mortals find themselves captive in the barn of two crazy French hot-air balloon inventors. Enter the daughter of a rag merchant and admirer of Harvey who helps the four escape. Along the way they learn the ups and downs of hot-air ballooning and discover a link between their project and the magic puzzle. But then a thunder storm hits and they are in trouble - will they make it back to Westbridge before lightening strikes?