While on a trip to Florida, John Martin stumbles upon the legendary fountain of youth. Willing to test the waters, John sips a handful of the liquid. The consequences are unforeseeable, for he begins to revert to his childhood on certain times that are neither predictable nor controllable, causing many problematic situations for John and his family.

Big John is cast as Captain Hook in his school's production of Peter Pan, while Little John ends up having to play Peter Pan at the same time.

John tries a new formula in the laboratory that he hopes will cure him from his conversions.