The heroes of the family adventure comedy 3 Ninjas return in this sequel (though not all of them are played by the same actors). Rocky (Sean Fox), Colt (Max Elliott Slade), and Tum Tum (Evan Bonifant) are three brothers whose Grandfather (Victor Wong) is a ninja master teaching them martial arts skills. The boys' Little League team has a big game coming up, but before they can hit the diamond, they have to help Grandpa return a sacred Ninja dagger to Japan. However, one of Grandpa's longtime enemies, now a wealthy and ruthless businessman, plans to steal the knife, and the boys are sent on a mission to Japan to rescue the valuable weapon. At first the tycoon sends his inept nephew to face off against the young Ninjas, but when that plan fails, Rocky, Colt, and Tum Tum are met by a team of trained warriors, who to their surprise are led by a teenage girl named Miyo (Caroline Junko King). Miyo soon strikes up a friendship with the brothers who are supposed to be her sworn enemies, and with her help they recover the knife and teach her a few things about baseball that come in handy when the big game finally rolls around.
by Mark Deming synopsis