Hidetora Ichimonji, a powerful though now elderly warlord, decides to divide his kingdom among his three sons: Taro, Jiro, and Saburo. Taro, the eldest, will receive the prestigious First Castle and become leader of the Ichimonji clan, while Jiro and Saburo will be given the Second and Third Castles. Hidetora is to retain the title of Great Lord and Jiro and Saburo are to support Taro.
Hidetora begins to lecture his sons about the importance of unity using three arrows. He selects one arrow out of a quiver and shows how easy it is to snap in half but three arrows bundled together are much more durable. Saburo, however, breaks all three arrows with his knee and calls the lecture foolish. He points out that Hidetora is foolish if he expects his sons to be loyal to him, reminding him that even Hidetora had previously used the most ruthless methods to attain power. Hidetora hears the comments as being subversive, and when his servant Tango comes to Saburo’s defense, he exiles both men. Fujimaki, a visiting warlord who had witnessed these events agrees with Saburo’s frankness, and invites him to take his daughter’s hand in marriage.
Following the division of Hidetora’s lands between his remaining two sons, Taro’s wife Lady Kaede begins to urge her husband to usurp control of the entire Ichimonji clan. She is still bitter about the loss of her family; Hidetora’s army had previouslly killed her family after a land dispute and then assimilated the family’s lands. When Taro demands Hidetora renounce his title of Great Lord, Hidetora then storms out of the castle and travels to Jiro’s castle, only to discover that Jiro is only interested in using Hidetora as a titular pawn. Hidetora and his retinue then leave Jiro’s castle as well without any clear destination. Eventually Tango appears with provisions but to no avail. Tango then tells Hidetora of Taro’s new decree: death to whoever aids his father. At last Hidetora takes refuge in the Third Castle, abandoned after Saburo’s forces followed their lord into exile. Tango does not follow him. Kyoami, the court fool, then jokes about Hidetora’s predicament, only to be thrown out of the Third Castle.
Shortly thereafter, Hidetora and his samurai retinue are besieged militarily by Taro and Jiro’s combined forces. As Taro and Jiro’s forces storm the castle, Taro is killed by a bullet fired by Jiro’s general, Kurogane. In a short but violent siege, Hidetora’s defenders are slaughtered and the Third Castle is destroyed by fire. Hidetora is allowed to survive though without any supplies or bodyguards and he succumbs to madness after wandering away from the decimated castle. Hidetora is discovered wandering in the wilderness by Kyoami and Tango, who are still loyal to him, and stay to assist Hidetora. In his madness, Hidetora is haunted by horrific visions of the people he destroyed in his quest for power. They take refuge in a peasant’s home only to discover that the occupant is Tsurumaru, the brother of Lady Sué, Jiro’s wife. Tsurumaru had been blinded and left impoverished after Hidetora took over his land and killed his father, a rival lord.
With Taro dead, Jiro becomes the Great Lord of the Ichimonji clan, enabling him to move into the First Castle. Upon Jiro’s return from battle, Lady Kaede, seemingly unfazed by Taro’s death, manipulates Jiro into having an affair with her, and undermines Jiro’s power from behind his throne. Kaede demands that Jiro kill Lady Sué and marry her instead. Jiro orders Kurogane to do the deed, but he refuses, seeing through Kaede’s perfidy. Kurogane then warns Sué and Tsurumaru to flee. Tango, still watching over Hidetora with Kyoami, encounters two ronin who had once served as spies for Jiro. Before he kills them both, one of the ronin tells him that Jiro is considering sending assassins after Hidetora. Alarmed, Tango rides off to alert Saburo. Hidetora becomes even more insane and runs off into a volcanic plain with a frantic Kyoami in pursuit.
Saburo’s army crosses back into Jiro’s territory to find him. News also reaches Jiro that two rival lords allied to Saburo (Ayabe and Fujimaki) have also entered the territory and Jiro hastily mobilizes his army. At the field of battle, the two brothers accept a truce, but Saburo becomes alarmed when Kyoami arrives to tell of his father’s descent into madnesss. Saburo goes with Kyoami to rescue his father and takes ten warriors with him; Jiro sends several gunners to follow Saburo, offering a bounty for whoever kills him and Hidetora. Lady Kaede has already convinced Jiro to send another group of assassins to hunt down Sue and Tsumuraru.
Jiro then further orders an attack on Saburo’s much smaller force and Saburo’s army retreats into the woods. Jiro attempts to pursue Saburo’s army in the forest but is stopped short with significant losses due to the deadly muskets wielded by Saburo’s infantry. In the middle of the battle a messenger arrives with news that a rival warlord, Ayabe, is marching on the First Castle, forcing Jiro’s army to hastily retreat.
Saburo finds Hidetora in the volcanic plain; Hidetora partially recovers his sanity, and begins repairing his relationship with Saburo. However, one of the snipers Jiro had sent after Saburo’s small group shoots and kills Saburo. Overcome with grief, Hidetora dies. Fujimaki and his army arrive from their victory only to witness Tango and Kyoami lamenting the death of father and son.
Meanwhile, Tsurumaru and Sué arrive at the ruins of a destroyed castle but inadvertently leave behind the flute that Sué previously gave Tsurumaru when he was banished. She gives a picture of Amida Buddha to him for company while she attempts to retrieve the missing flute. It is when she returns to Tsurumaru’s hovel to retrieve it that she is ambushed and killed by Jiro’s assassins.
At the same time, Ayabe’s army pursues Jiro’s army to the First Castle and commences a siege. When Kurogane hears that Lady Sué has been murdered by one of Jiro’s men, Kurogane confronts Kaede. She admits her perfidy and to her plotting to exact revenge against Hidetora and the Ichimonji clan for having destroyed her family years before. Enraged, Kurogane kills Kaede. Jiro, Kurogane, and all Jiro’s men subsequently die in the battle with Ayabe’s army that follows.
A solemn funeral procession is held for Saburo and Hidetora. Meanwhile, left alone in the castle ruins, Tsurumaru trips, dropping the Amida Buddha image Sué had given to him. The film ends with a distance shot of Tsurumaru, blind and alone, silhouetted against the castle’s landscape atop the ruins.