After the Pearson family arrive at their dream vacation house in Michigan, the children discover a friendly alien living in their attic. However, he lives with three other aliens that are attempting to rule the universe. The plot mainly revolves around the children in the Pearson family having to defend their vacation house. Much of the comedy is derived from the aliens being able to occupy the minds of adults, and turn them into "space zombies". The kids, however, are immune. As Ricky has lied about his age, he quickly succumbs to the alien mind control, with predictably funny behaviour and actions. The kids must therefore forget their differences and start working together to defeat the aliens. Tom is anxious to cast off his "geeky" image, so much so he deliberately starts to fail at math, much to his Dad's chagrin. This causes them to clash often. Bethany is besotted with Ricky, who is a no-good womaniser, preying on younger girls. Tom and his cousin Jake could not be more different, but, by the end of the movie, they have both learned something from each other.