Meet Samuel, Jeffrey and Michael Douglas! Their grandfather, Mori Tanaka, is highly skilled in the fields of Martial Arts and Ninjitsu. And for years he's been training these boys this technique. He even gave them names: Rocky because he's "solid and cool as granite rock"; Colt, because he's "fast and free, a spirit of a young wild horse"; and Tum Tum because ambition begins and ends with his tummy". But one day, an old "friend" of Grandpa's, Hugo Snyder, is heard from again. He's being hassled by the FBI, and the boys' father happens to be an FBI officer. So Snyder figures if he kidnaps the father's kids, it will ease the tension, none of his own men are suitable for the task, so he hires three dim and incredibly incompetent surfers to do the deed. The boys treat them to a night of Ninja moves and hilarious gags, ala Home Alone. But the boys soon get captured by Snyder, and what is more, they (especially Colt) becomes doubtful of their grandfather, until Grandpa bursts into action and fights Snyder.