The story takes place in the 1940s, in a fictional Japan, where the country is dominated by the upper class and the country suffers from a huge income disparity between the rich and poor. During this time, an evil masked villain named "K-20" roams around Japan stealing priceless artifacts. Always on the trail of K-20 is his arch nemesis Akechi - a suave detective. When Akechi announces his engagement to the rich heiress Yoko Hashiba, K-20 warns Akechi to call off the wedding, or he'll be there to make his biggest heist yet. Meanwhile, a good-natured circus performer named Keikichi Endo is hired by a mysterious figure to snap photos of Akechi and Yoko's wedding. Keikichi is unaware that his employer is, in fact, the evil K-20 and he's being set up to be his fall guy.