Lessons in the art of espionage aboard Mademoiselle Geraldine's floating dirigible have become tedious without Sophronia's sootie Soap nearby. She would rather thwart dastardly Picklemen, yet her concerns about their wicked intentions are ignored.
Who can she trust? Only one thing is certain: a large-scale plot is under way. Sophronia must be ready to save her friends, her school, and all of London from disaster.