A Swiss orphan is heartbroken when she must leave her beloved grandfather and their happy home in the mountains to go to school and to care for an invalid girl in the city. Illustrated notes throughout the text explain the historical background of the story.
Basil leads an expedition up a towering Swiss mountain in search of a colony of mice who have been missing for centuries, but before he can solve the mystery he must confront a mysterious snow mouse and evil Professor Ratigan.