Each year, three brothers Samuel, Jeffrey and Michael Douglas visits their Japanese grandfather, Mori Shintaro whom the boys affectionately refer to as Grandpa, for the summer. Mori is a highly skilled in the fields of Martial arts and Ninjutsu, and for years he has trained the boys in his techniques. After an organized crime ring proves to be too much for the FBI, it's time for the 3 brother NINJAS! To use their martial arts skills, they team up to battle the crime ring and outwit some very persistent kidnappers!

Fun-loving Annabelle Andrews and her uptight mother, Ellen, have a hard time getting along with each other. One Friday the 13th, they both wear magical necklaces that make them switch bodies for the day.