Lethal Ninja gets off to a rollicking start with some mysterious business types making an unknown getaway by car. After someone delivers the immortal line, "Tell them to stop the ninjas," it becomes silly action central. A bunch of ninjas appear, chasing the car on foot, and using whatever nifty ninja tricks they have to prevent the getaway. Things go bad, the ninjas prevail and a Dr. Kikuchi gets beheaded. Kikuchi's noggin gets taken to evil bastard Mr. Brian, who applies blatantly fantastic computer technology to steal secrets from Kikuchi's brain. Brian strip-mines Kikuchi's brain to find the key to opening a special red box that contains the secret of "Jinrui," a MacGuffin said to cure any disease, including all manner of STDs and even the common cold. Mr. Brian wants to use the cure to make a fortune, and with a bunch of ninjas at his side, success must be in the offing.