Twin fifteen-year-old New Yorkers Tom and Mitch like to spend their free time skateboarding and reading comics, until one day they are attacked by a thug in ninja gear. They then learn that their father and live-in-butler are members of a crime-fighting organization called R.O.N.I.N., that their father is in danger, and that they have been recruited to join their father's clan. This sets the brothers off on the adventure of a lifetime.