Idaville's secret weapon against lawbreakers, ten-year-old Encyclopedia Brown, assists the police force with ten insoluble cases. Solutions are at the back of the book.
The Alden children investigate various mix-ups at a zoo run by their grandfather's friend in an effort to save it not only from pranksters but also from the town council.
The Alden children suspect that the other guests are somehow involved when things begin to disappear at the bed and breakfast where they are staying in Washington, D.C.