Ben, Zara, Sam, and Marcia begin their summer vacation by helping Professor Ampersand and a new friend build the Silver Turtle, a futuristic airplane, but on the day the first test flight is planned, a strange woman steals the airplane with the children inside.

In a country far away, a new invention--the mechanical mousetrap--has caused all the mice but one to flee to America. Now stranded in a dangerous country, the last mouse decides to build a plane and fly to the land of freedom.