In Montana in 1882, "Boss" Spearman (Robert Duvall) is an open range cattleman, who, with hired hands Charley Waite (Kevin Costner), Mose (Abraham Benrubi), and Button (Diego Luna), is driving a herd cross country. Charley is a former soldier who served in a "special squad" during the Civil War and feels guilty over his past as a killer of both enemy soldiers and civilians. Once out of the army, he worked for men like Baxter and isn't super proud of it. Button is the youngest of the group and a greenhorn. He cheated at cards and earned the ire of Charley.Boss sends Mose to the nearby town of Harmonville for supplies. The town is controlled by a ruthless Irish immigrant land baron, Denton Baxter (Michael Gambon), who hates open-rangers. Baxter is a rancher himself and has built himself a large cattle empire. Free rangers damage his business by providing competition and he hates that. Mose is badly beaten and jailed by the marshal, Poole (James Russo). The only friendly inhabitant is Percy (Michael Jeter), the livery stable owner.Boss and Charley become concerned when Mose does not return. They retrieve him from the jail but not before getting a warning from Baxter about free grazing on his land. Baxter wants Boss and his crew out of the county asap. He allows Poole to release Mose to Boss. Mose's injuries are so severe that Boss and Charley take him to Doc Barlow (Annette Bening). There they meet Sue Barlow. Charley is attracted immediately but assumes that Sue is the doctor's wife. Mose had a couple of broken ribs.After catching masked riders scouting their cattle, Boss and Charley sneak up on their campsite in the night (They reckon Baxter wants to assimilate their herd or scatter it to the wind. so, their only choice is to fight or flight.) and disarm them. At the same time, another attack results in Mose's and his dog's death. Button is badly injured and left for dead. Charley and Boss vow to avenge this injustice. Charley convinces Boss to first save Button by taking him to the doctor.They leave Button at the doctor's house (Sue was alone at home and does some prelim checks on Button to ascertain that his skull is not fractured, but his is concussed really bad. Doc Barlow (Dean McDermott) had been summoned by Baxter to look after his men, who had some trouble in the woods 2 nights ago) and go into town (it's raining heavily and its already nightfall. They end up saving the life of a dog in the flooded streets).Charley and Boss run into Poole at the local cafe, where Poole announces that he has a warrant for their arrest for assaulting Baxter's men. Boss announces that Baxter's men shot & killed Mose and injured a 16 yrs old Button. He says they have no quarrel with the town folks but will take revenge on Baxter.Charley and Boss return to Sue's for the night and to check on Button. Boss reveals that he used to have a family, that died in an epidemic and since then he has never been back home. Charley learns that Sue is the doctor's sister, not his wife. He declares his feelings for her, and she gives him a locket for luck. Charley leaves a note with Percy, in which he states that if he should die, money from the sale of his saddle and gear are to be used to buy Sue a new tea set, having accidentally destroyed her previous set during a "flashback" episode.Boss and Chrley head back into town and get a warning from Percy that Marshall's men are waiting for them at the stables, and in their carriage, while Marshall himself is in the jail, all alone, waiting for them to be brought in. Boss and Charley lock Poole in his own jail. Boss knocks him out with chloroform he has stolen from the doctor's office. The deputies are also locked up, and Boss knocks out each one with the chloroform as well. They check on Button again and have breakfast with Sue before heading back into town to face Baxter and his men. Boss buys some chocolate and cigars at the store before taking their positions.Boss and Charley are pitted against Baxter and his men. Before the fight begins, Charley confesses to Boss that his full name is Charles Postlewaite, and he asks Boss to reciprocate. Boss says his real name is Bluebonnet Spearman, but makes Charley swear not to tell anyone. As Baxter and his men approach, Charley confronts them and shoots Butler (Kim Coates), the hired gunman who shot Button and killed Mose. An intense gun battle erupts in the street, with Boss, Charley and Percy outnumbered before the townspeople begin to openly fight against Baxter (Hearing the gunfight Sue comes into town and is captured by one of Baxter's men. This brings the townsfolk out as they all have huge respect for Sue and her brother). After being injured, Baxter had headed back to Sue's house only to find Button there. He gets Button into town and forces Boss and Charley to come out in the open. A stalemate ensues till Button starts the shooting. After an intense firefight, Baxter's men, to include Marshal Poole and his deputies, are dead and Baxter ends up wounded and alone, trapped in the jailhouse. Boss shoots open the jailhouse door and engages him in a brief close-quarters gunfight which leaves Baxter mortally wounded.Sue's brother tends to the wounded townspeople and open rangers. Charley speaks to Sue in private, telling her he must leave. She counters that she has a "big idea" about their future together and that she will wait for him to return. He does return, and proposes to Sue, who accepts. After Button has recovered, Charley and Boss decide to give up the cattle business after delivering their current herd, and settle down in Harmonville, taking over the saloon.