Wayne Szalinski's career and marriage are on shaky ground. His latest invention, a shrink ray, blows things up instead of shrinking them. But when a neighbor hits a baseball through the attic window, all that changes. But Wayne isn't the one who first discovers it works. When he comes home, in a rage he damages the shrink ray and unknowingly throws out his shrunken kids and the neighbors shrunken kids who face a jungled back yard full of danger to get home.