The Mad Inventor creates a fiendish device called the Monstermobile. First he uses it to rob an armored truck and then he uses this machine to rob the money plates from the U.S. Mint and starts to get away. Buzz activates Frankenstein Jr. and they take off after the crook. The Mad Inventor tries several devices to stop Frankie, but they all fail. Then he captures Buzz and this really makes Frankie mad. Frankie rescues Buzz and destroys the Monstermobile and also gets back the plates. They drop off the villain at a jail and return the money plates to the U.S. Mint and the day is saved.