Three frightfully clever English children, visiting a theatrical costuming aunt while their parents vacation, set out to discover who's ambushing her big orders. The proceedings are strictly cloak-and-dagger, without a fresh face in the entire cast. Of course, aunt, uncle and cousin know nothing of the children's investigations except when policemen bring them home on various occasions. Oldest Nicola counsels Crispian and Candy: ""After all, we're only children. And it's only in books that children catch burglars and solve mysteries and beat the police to things"". This is one of those books.