Hidetora Ichimonji, a powerful but 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. However, Saburo is exiled after criticizing his father's lecture about unity. Hidetora's servant Tango is also exiled for defending Saburo.
Following the division of Hidetora's lands between his remaining two sons, Taro's wife, Lady Kaede, still bitter about Hidetora killing her family and taking their land, successfully urges him to usurp control of the entire Ichimonji clan. When Taro demands Hidetora renounce his title, Hidetora leaves and travels to Jiro's castle, only to discover that Jiro is only interested in using Hidetora as a titular pawn. As Hidetora and his retinue wander, Tango warns Hidetora of Taro's new decree: death to whoever aids his father. Hidetora plans to take refuge in the Third Castle, which was abandoned by Saburo's forces (who followed him into exile) and taken over by Taro's general Ogura. Hidetora feels they can take Ogura easily, whereas Kyoami, the court fool, jokes about Hidetora's predicament, and is yelled at by Hidetora to stay behind if he's afraid. Kyoami and Tango stay outside while Hidetora and the rest of his retinue take refuge in the Third Castle, which they find unoccupied.
Later, Hidetora and his retinue are attacked by Taro and Jiro's combined forces - Taro's men had "abandoned" the castle to lure Hidetora into a false sense of security and ambush him. Taro is killed by a bullet fired by Jiro's general, Kurogane. All of Hidetora's retinue are either killed or commit ritual suicide. Hidetora is allowed to survive and succumbs to madness as he wanders away from the destroyed castle. Kyoami and Tango, still loyal to Hidetora, find him and stay to assist. Hidetora is haunted by visions of the people he killed in the past. They take refuge in a peasant's home only to discover that the occupant is Tsurumaru, the brother of Lady Sue, Jiro's wife. Tsurumaru's eyes were gouged out by Hidetora's forces and he was left impoverished due to Hidetora's siege. With Taro dead, Jiro becomes the Great Lord of the Ichimonji clan, and moves into the First Castle. Lady Kaede manipulates Jiro into having an affair with her, and demands that he kill Lady Sue, and marry her instead. Jiro orders Kurogane to do the deed, but he refuses, seeing through Kaede's perfidy. Kurogane then warns Sue and Tsurumaru to flee. Tango encounters former spies and before killing them, he is informed that Jiro is considering sending assassins after Hidetora. Tango rides off to alert Saburo. As his madness grows, Hidetora runs off into a volcanic plain.
After Saburo's army enters Jiro's territory to find Hidetora, Jiro hastily mobilizes his army. After a truce, Saburo learns from Kyoami of Hidetora's potential location. After Saburo leaves, Jiro attacks Saburo's smaller forces, suffering losses, and orders his remaining forces to retreat after learning of another army marching on the First Castle. Saburo finds Hidetora, who partially recovers his sanity, and reconciles with Saburo. However, Saburo is killed by one of Jiro's snipers. Hidetora dies from grief. Tsurumaru and Sue arrive at the ruins of a castle, but inadvertently leave behind the flute that Sue gave him when he was banished. She gives him a picture of Amida Buddha for protection while she attempts to retrieve the flute. However, she never returns.
As the First Castle is besieged, Kurogane learns of Sue's death, and confronts Kaede. After she confesses her plot was revenge against the Ichimonji clan, she is killed by Kurogane. Jiro, Kurogane, and all Jiro's men subsequently die in battle. A funeral procession is held for Saburo and Hidetora. Meanwhile, left alone in the castle ruins, Tsurumaru trips, dropping the Amida Buddha image Sue had given to him. The film ends with a distant shot of Tsurumaru silhouetted against the castle's landscape atop the ruins.
