Andrew, his cousin Judy, and Thudd the robot, having been shrunk by a shrinking machine, encounter many terrifying creatures, including Mrs. Scuttle, as they try to reach the Atom Sucker before it explodes.

Still reduced to the size of insects, Andrew, Judy, and the robot Thudd go to a pond, where they encounter dragonflies, moss animals, and fierce larvae in an attempt to learn why frogs are disappearing throughout the world.