Around Ginza there is a night-city of bars and cabarets, hostesses, customers. Assisting to keep order here is Kagari (Akira Kobayashi) who specializes in the women, their problems and troubles. He has saved many a girl from blandishments of pimps, makes customers pay up and women play straight. So he is called 'the woman's police-man' and he takes his job seriously. One day, Chiyoko (Yukiyo Toake), a former hostess, comes to him. Her husband has been murdered and she wants help. The man had been a college classmate and Kagari decides to do what he can. In his investigation he overturns a whole nest of intrigue. Men he had thought irreproachable turn out to be corrupt; solid citizens are seen as the worst kind of scoundrels. Until now, Kagari has specialized in women and their problems. But, realizing the real state of affairs, he rolls up his sleeves for a good cleaning- up-at the same time discovering the murderer of his friend.

Nezumi Kozō is the nickname of Nakamura Jirokichi, a Japanese thief and folk hero who lived in Edo during the Edo period. His exploits have been commemorated in kabuki theatre, folk songs, jidaigeki, and modern pop culture.

A series of murders has been committed by someone with a new model gun, a Mord-Gessel X 38. Indeed, Daisuke himself is almost killed while investigating the case. This occurred while he was with Ritsuko, daughter of a company president. Detective Kimura thinks that the president himself, returned to Japan after an absence of fifteen years, might be the killer, or at least the man who supplied the gun. Ritsuko's father limps and though she explains this as the result of a traffic accident, Kimura remembers a narcotics smuggler named Suginami who shot himself in the ankle and then escaped from the hospital. He believes that the company president and the drug peddler are the same.