While sitting on the plane, on their way to Paris, France for the holidays, "Kate" and "Harry McCallister" realize that they've forgotten their youngest son "Kevin" at home in the suburbs of Chicago. While counting her kids she mistakes one of the neighbor´s kids for one of her own. Thinking that all of her kids are accounted for, the family boards the plane without hesitation. After realizing that their son is missing, "Kate" tries everything in her power to get back to "Kevin" as quickly as possible.