When the villainous Mr. Wink and Mr. Fibb extend the adult swim time in the neighborhood pool, the Kids Next Door are sent a red alert to stop them. Numbuh One suggests employing the Kid-A-Pault, a Kid's Next Door weapon to put an end to this tyranny...But their plan fails, leaving them to find other means of battling Mr Wink and Mr Fibb.

The villains of the Kids Next Door, lead by Father, join forces to resurrect the Ultimate Evil, Grandfather, a tyrant who once ruled the world many years ago when most of the villains were themselves kids. However, Father disgraced him that he can't even try to destroy the KND and the Villains were quickly betrayed when they are turned into Senior Citizombies, creatures that are immortal and can transform any living creature into one of them and slaves who are forced to make Tapioca to refuel Grandfather so he can find and destroy the Book of K.N.D.