Paladin is killing a little time while waiting for his current enamorata to get herself primped up. His attention is grabbed by the news of a potential range war between the DeVries brothers. He immediately starts to prepare to send his card to...someone. His agitation is made clear by the fact that he cancels his evening with the young lady, although it isn't strictly necessary--he's going to have to wait for a reply, after all. (San Francisco must be full of women pining for Paladin--and an equal number wanting to hit him.) We see further evidence of Paladin's upset--normally his penmanship is a very fine hand, but the message on the back of his card--"IOU a Debt" is done in a clumsy scrawl.
The elder DeVries, Walt, is a cattleman, while the younger, Tony is a farmer--as are the majority of the citizens in the area. Walt's cattle are constantly damaging the farmers' crops, so they plan to string barbed wire to protect their land--which seems a reasonable thing to do, but Walt does not agree. Paladin arrives in town to find a trio of Walt's men harasssing a young ranch hand who works for Tony DeVries and his wife--who apparently is not well regarded by Walt's men. Paladin rescues the boy, and travels with him to Tony's homestead.
Tony had saved Paladin's life in the past. It would have been interesting to learn the details, but the only hint is that it was apparently during the Civil War. Tony wants Paladin to clear the debt by killing Walt, feeling that this is the only way to settle the matter. Elizabeth, Tony's wife, had been engaged to Walt, a man nearly twice her age, until she got a look at younger brother Tony. She and Tony both acknowledge that they treated Walt badly, but it's a done deal and can't be changed. Walt not only beat Tony to a pulp--which Tony conceded was his right--he then tied his brother up and whipped him until he broke down, leaving him with physical and emotional scars.
Walt refuses to get past the hurt done to him by his brother and fiancee, but his bitterness is affecting far more than just his kin. He acts as if all the land is his alone, the settlers being annoying encumbrances to be trodden down. On his way to see Walt, Paladin sees evidence of the poverty and resentment Walt is causing. Paladin's rationality and eloquence fail him--Walt will make no concessions whatsoever. His point of view is that a man is a winner or a loser, and if a man is a loser, he is absolutely nothing at all. Backing down would make him a loser. He makes it clear that he will kill anyone who tries to string barbed wire (where are the legal authorities in all of this?) and also indicates that if Paladin helps his brother, he will whip Paladin until he breaks down, too.
Paladin and Tony return from riding Tony's property to find his young ranchhand dead and the house full of Walt's men and Walt himself. Paladin is disarmed. Unable to do anything, Tony and Elizabeth drive helplessly away as their home is set on fire. Paladin turns to go as well, but is brought up short by Walt's whip. It doesn't take him long to get the upper hand, retrieve his main gun and escape. Walt orders his men to find him and kill him.
Paladin barricades himself in a neighbor's barn, brusquely refusing the man's offer to help. He shoots Walt's main henchman, and discovers that the other men are not particularly happy with Walt's actions. He tells them that he will await Walt in town.
The ending gets rather confusing. Tony had earlier stated that he wanted Paladin to kill Walt. When Walt arrives in town, Paladin strongly implies that Tony has asked him not to kill him (which I suppose is possible) and that he will only kill Walt if Walt forces him to. Getting Walt's whip, Paladin actually only strikes one blow with the business end--the remainder of the fight is hand-to-hand. He begs Walt to simply allow his neighbors to live and work in peace. Walt agrees--but only because Paladin has defeated him, and thereby, in his eyes, Paladin has destroyed him. He's left a completely broken man. Tony and Elizabeth seem to regard the situation with pity, although Tony states that it had to be done. This seems true enough--it doesn't seem likely that Walt would have backed down any other way, and it wasn't Paladin's fault that Walt allowed one fight to wreck his life. Paladin's final comment to Tony makes it sound as though he is disgusted with him, and will henceforth have nothing to do with him. He seems to have forgotten that he was the one who offered to help in the first place. And everyone seems to have forgotten that a young boy was murdered in the course of this.