When a world-famous astronaut returns home from his latest mission, he brings a unique souvenir to his wife and two children: a piece of an asteroid that hit his space station. But soon, strange things start to happen in the neighborhood, and nine-year-old Katie becomes convinced that aliens have moved in next-door. Armed with a vivid imagination- and the help of neighborhood "weirdo" Old Man Nelson- Katie embarks on a mission to save the world from a galactic invasion.