The narrative unfolds in Japan during the 1860s, a significant period marked by cultural consolidation. Two samurai, Munezo Katagiri, played by Masatoshi Nagase, and Samon Shimada (Hidetaka Yoshioka), bid farewell to their companion Yaichiro Hazama (Yukiyoshi Ozawa), who is set to serve in Edo (now Tokyo) under the local shogunate. Though this position is coveted, Katagiri expresses his unease about Yaichiro's character and foreshadows trouble when Yaichiro, already married, reveals his intention to indulge in Edo’s pleasures during his stay.
Later that evening, during a dinner gathering, Katagiri’s mother shares their family's ongoing financial struggles since the tragic death of her husband—a consequence of financial scandals tied to a construction project, leading him to commit ritual suicide. She hopes for a match between Samon and Shino (Tomoko Tabata), Katagiri’s sister. Also in attendance is Kie, brilliantly portrayed by Takako Matsu, the literate housekeeper of the Katagiri household. In a reflective voiceover, Katagiri hints at his deeper feelings for Kie, but soon confesses that around the time Shino weds Samon, Kie marries a man from the merchant class and departs from their lives.
As the years roll on, Katagiri faces personal tragedy with the death of his mother. While wandering the streets, he unexpectedly spots Kie, who is working in a kimono shop, assuring him of her well-being. However, Shino soon informs Katagiri that Kie has been subjected to relentless duties within her new family, essentially reduced to a slave, and her health is alarmingly fragile. Determined to help, Katagiri visits Mrs. Iseya (Sachiko Mitsumoto), Kie’s mother-in-law, only to find Kie in a state of delirium due to her illness. Fueled by rage, he confronts Kie’s husband to demand a divorce, bringing her back to his home to aid her recovery.
As the world around them evolves, Katagiri and his fellow samurai must adapt to Western fighting techniques, which the clan's elders scorn. News reaches them from Edo about a suppressed rebellion against the shogunate, with Yaichiro’s involvement raising alarms. Following a grim twist of fate, Yaichiro is returned to the village in chains, denied the honor of ritual suicide, and doomed to spend his days imprisoned. When the clan's chief retainer, Hori (Ken Ogata), demands that Katagiri identify those who supported Yaichiro, Katagiri resolutely refuses, standing by his samurai honor and facing dismissal from the clan.
Meanwhile, Kie regains her strength and returns to her duties as Katagiri's housekeeper. Though there is an undeniable bond between them, the constraints of their social classes loom large, compelling them to maintain a distance. However, due to escalating gossip, Katagiri decides to send Kie away to live with her father in the countryside. Shortly thereafter, Yaichiro escapes captivity and takes hostages from a family, prompting Hori to insist that Katagiri eliminate him.
Knowing that Yaichiro surpasses him in skill, Katagiri seeks wisdom from their former mentor (Min Tanaka), who has since become a farmer and imparts a risky tactic involving turning one's back on an opponent. When the time comes, Katagiri approaches the outskirts of the village, attempting to persuade Yaichiro to surrender. Yet, when Yaichiro rejects his pleas—blaming Hori and the leaders for their incompetence—an intense duel ensues. Katagiri manages to inflict a serious wound but as fate would have it, Yaichiro is ultimately gunned down by hidden soldiers in the woods. This ignoble death weighs heavily on Katagiri who knows it brings shame to samurai honor. Confronted by Yaichiro’s wife (Reiko Takashima), he learns of her desperate bargain with Hori, exchanging favors for false assurances of her husband’s safety. Bound by an oath of suicide should Yaichiro die, she tragically takes her own life.
Conflicted about his loyalties, Katagiri approaches Hori and reveals his suspicions, only to witness Hori’s brutal candor about the preceding chaos. Reckoning with the injustice faced by the Hazama family, Katagiri exacts revenge by plunging a thin blade into Hori's heart—a method referred to as “the hidden blade,” leaving nearly no evidence. He then pays his respects by burying the blade at the grave of the Hazamas, signifying his deepest regret, and renouncing his status as a samurai. Finally, seeking a different path, he resolves to become a tradesman and departs for the island of Ezo (modern-day Hokkaido). Before his departure, he visits Kie one last time, and with their social differences finally set aside, he proposes to her. Kie joyfully accepts, and the film concludes with the two hand in hand on a scenic hilltop, gazing toward their hopeful future together.
