During a championship baseball game, the three boys learn that their grandfather is in peril in Japan and rush out to assist him, forfeiting the game. When they arrive in Japan, they must use all of their abilities to protect him from an old foe who has returned to seek vengeance.
The three underage ninjas find themselves in the heart of martial arts mayhem after accompanying their grandfather to Japan. Rocky, Colt, and Tum Tum are up to their ears in high-kicking action and rapid-fire comedy as they are pursued by a moronic trio of brain-dead robbers and an army of well-trained ninjas. Because of the growing trend in family films, experienced South Korean filmmaker Simon Sheen opted to blend the theme of Asian martial arts with an American children's comedy for his first American feature.