What kind of a nanny wears a motorcycle jacket, mirrored sunglasses, and a straw hat with flowers on top? When ten-year-old Ali and eight-year-old Jake find out that an odd woman who calls herself Nanny X is going to care for them, they're worried. They see her speak into a diaper. Even weirder, the diaper actually seems to be answering her. Everything begins to make sense when the kids discover Nanny X's secret identity. It turns out that Ali, Jake, and their toddler sister are in for a wild ride as they help Nanny X with a mysterious mission.