A police detective has his gun stolen and with a partner tracks down the man who is using it to commit robberies and murder.
Detective Murakami (Toshiro Mifune) is on a bus when he is robbed. He runs after the thief, but he gets away. Murakami reports that his pistol was stolen, and Inspector Nakajima sends him to the pick-pocket department, where they tell him of a woman suspect. Murakami finds the woman, talks with her, and follows her. She tells him to see gun dealers.
Murakami searches in various places while wearing an old uniform. He demands food from a woman and lays down to rest. A man offers to sell him a gun for his rice ration book. Murakami goes to the meeting, and a woman (Fumiko Honma) offers the trade. He asks for a Colt, and she explains how the business works. He arrests her.
Inspector Nakajima tells Murakami that a woman was murdered with a Colt. Murakami finds one of his spent bullets and gives it to the forensic expert, who says it was his gun. The Inspector assigns Murakami to work on the case with the experienced detective Sato (Takashi Shimura). Murakami finds Sato questioning the woman, and she describes Honda, who is a baseball fan. Murakami blames himself because of the gun.
Sato and Murakami go to a baseball game. A vendor using a photo finds Honda. They page Honda and arrest him. They learn that the ration book belonged to Yusa, and they look for him. Sato and Murakami ask the bellboy Sei about Yusa, and he says that the line dancer Harumi is his friend. When Sato questions Harumi Namaki (Keiko Awaji), she cries.
Sato invites Murakami to his home, and they discuss their philosophies. Another woman has been murdered, and her husband is upset and cries. Sato tells Murakami that it was Yusa's bullet. Sato says that Yusa is like a mad dog.
Sato and Murakami learn that Harumi is not working, and they go to her home. She refuses to talk, but her mother (Eiko Miyoshi) says that Yusa just left. Murakami stays and gives Sato his gun. Sato goes to a hotel. Harumi shows Murakami a dress that Yusa bought her. Sato follows leads and questions people. Harumi puts on the dress, and her mother rips it. Harumi cries. Sato is led to another hotel. He calls for Murakami and mentions Harumi, who is summoned to the phone. Sato is shot.
At the hospital Murakami is upset and waits. The woman tells him that Yusa will be at the station. There Murakami sees him but realizes that Sato has his gun. Murakami chases Yusa into the woods. Yusa has his gun and shoots Murakami in the arm, then misses twice. They fight, and Murakami handcuffs Yusa, who screams in agony. Murakami visits Sato, who says there are many such cases.
This detective story reflects the desperation in post-war
Japan where some have turned to violent crime just as a stray
dog can become a mad dog.