Every year, 12-year old Samuel, 10-year old Jeffrey and 8-year old Michael Douglas visit their grandfather, Mori Tanaka at his cabin. Mori trains his grandchildren in the art of Ninjutsu. As the summer comes to an end, Mori gives each of them a new "ninja" name based on their personalities: 'Rocky', 'Colt', and 'Tum-Tum'.