Following beautiful, cinnamon-scented Natasha, adventurous Frederick and his food-loving brother, Ishbu, leave their comfortable classroom cage and travel through Scotland and northern Europe to rescue her father, Professor Ratinsky, from the clutches of the nefarious Big Cheese. As readers of The Mystery of the Burmese Bandicoot (2007) already know, these are no ordinary fifth-grade rats. Ishbu is loyal and determined, and Frederick can read. His inventive mind and extensive knowledge of geography make it possible for all four of them to escape treacherous show mouse Mo-mo, rat-terrier henchmen Snip and Snarl, and the blind possum Big Cheese himself. The story moves quickly, helped by cliffhanging chapter endings, but the author (a former teacher) packs in interesting incidental information and intriguing new vocabulary. An afterword offers more detail about topics as varied as show mice, mousetrap catapults and the San Francisco Chinese New Year Parade. A sequel that can stand alone, this lively adventure will appeal to able middle-grade readers who like to learn as much as Frederick does. (Fantasy. 8-12)