The story follows the young and arrogant doctor Noboru Yasumoto, who pursued his medical education at a Dutch medical school in Nagasaki. He dreams of achieving the esteemed role of personal physician to the Shogunate, a title currently held by a close relative. He expects to navigate his way through the elite and enclosed military structure of medical training. However, his journey takes an unexpected turn when he is assigned to a rural clinic under the mentorship of the esteemed Dr. Kyojō Niide, affectionately known as Akahige (or "Red Beard"). Despite his rough demeanor, Dr. Niide possesses a heart filled with compassion and profound wisdom.
Initially, Yasumoto is furious about this placement, believing there's little he can gain from working alongside Dr. Niide. He suspects that Niide is primarily interested in his credentials from Nagasaki and thus rebels, refusing to engage with patients, don his uniform, or even respect the clinic's austere environment. In his disdain, he strays into a forbidden garden where he encounters "The Mantis," a unique case under Dr. Niide's exclusive care. As the narrative unfolds, we discover that Yasumoto's previous fiancée, Chigusa, betrayed him, leading to the end of their engagement and feeding his resentment towards romantic bonds.
The film intricately weaves the lives of the clinic's patients into Yasumoto's story. Among them is Rokusuke, a man nearing death, whose hidden anguish becomes evident when his despondent daughter arrives. Another poignant tale is that of Sahachi, a beloved local figure whose life intersects tragically with his wife's demise, necessitating a brutal act unknowingly committed by him during her last moments. Under the mentorship of Dr. Niide Toshirô Mifune, Yasumoto is called to rescue Otoyo, a twelve-year-old girl trapped in a brothel, culminating in a fierce confrontation with local thugs. This pivotal moment marks the beginning of Yasumoto's transformation as he starts to humble himself and broaden his understanding of the world.
As fate has it, when Yasumoto becomes ill, Otoyo is asked to care for him, creating a reciprocal healing dynamic. During this period, Chigusa's younger sister, Masae Akemi Negishi, visits him, revealing that his mother is unwell and yearns for his presence. Through his mother, Yasumoto learns of Chigusa's new life and child with another man, compounding his emotional turmoil. Masae later crafts a kimono for Otoyo while suggesting that Yasumoto consider marrying her.
Through his intensive interactions with patients, Yasumoto begins to grasp the extent of suffering around him, recognizing his potential to alleviate pain and regret his prior egoism. A significant lesson unfolds when Chôbu, a local boy, is caught stealing from the clinic. Otoyo, showcasing her growth, befriends him, sharing the kindness she received from Dr. Niide and Yasumoto. Tension escalates when the brothel's madam attempts to reclaim Otoyo, yet the clinic staff stands united to protect her. In another act of desperation, when Chôbu's family chooses to ingest poison in their despair, the doctors mobilize to save them, demonstrating their commitment to their community.
In a compelling climax, Yasumoto is granted the coveted role of personal physician to the Shogunate. Despite revealing his engagement to Masae, he surprises everyone at the wedding by declining the prestigious position to remain at the clinic, choosing to serve the underprivileged alongside Dr. Niide. Though taken aback by his decision, Dr. Niide ultimately supports Yasumoto, recognizing the depth of his character growth and newfound purpose.
