On a sweltering summer day in a crowded Japanese city, a young detective's worst nightmare begins when he falls asleep on a bus and awakens to find his service pistol has been stolen. The detective, Shoichi Murakami, is a rookie haunted by the shame of his carelessness and the knowledge that his gun is now a deadly weapon in the hands of a criminal. The setting is a sweltering, post-war urban landscape, a place where the line between desperate survivor and hardened criminal is often blurred by the heat and the lingering trauma of recent history.

The police department orders Murakami to stand down, suspecting him of negligence or even involvement in gun smuggling, and assigns the weathered and world-weary Detective Sato to secretly resolve the matter within five days. Defying orders, Murakami cannot let the case go and begins a desperate, solitary hunt through the city's underbelly. His pursuit leads him to a former classmate from his middle school days, Ginji Yanashita, a pickpocket whose path has led him into a life of escalating crime. As Murakami closes in, he discovers that the stolen gun has passed from Yanashita to a more disturbed individual, a war veteran named Yusa whose experiences have left him fractured and dangerous. The investigation becomes a cat-and-mouse game through a world of pawn shops, boxing rings, and sweltering tenements, forcing Murakami to confront not just a criminal, but a dark reflection of his own post-war disillusionment. The seasoned Sato, acting as both mentor and leash, eventually joins the chase, leading to a tense, muddy climax in a field where the two detectives finally corner the desperate fugitive Yusa. The final confrontation leaves Sato wounded, and Murakami, having retrieved his gun, is left to sit with the uncomfortable understanding of how similar circumstances can produce a detective and a stray dog.