The three brothers are again spending the summer with their Grandpa and, naturally, looking around for some Ninja action. Soon they hear about evil Jack Harding, the owner of a waste management company, who's been illegally dumping toxic chemicals at the local Indian reservation, causing great sickness and even death. Their friend Jo's father has managed to find evidence against Harding and his illicit operations, but now he's disappeared and she strongly suspects he's been kidnapped. Armed with various make-shift weapons and in full Indian war-paint, the three Ninjas, plus Jo, sneak into the heavily armed Harding Waste Plant and rescue her dad. Celebrations at the reservation are cut short, however, when Harding and his rifle-wielding henchmen, "crash" the party. determined to get back the evidence against their operation.