Frank Harris, [Jack Lemmon], a Chicago hotel clerk, dreams of striking it rich in cattle and has fallen for Maria Vidal, [Anna Kashfi], the daughter of hotel guest and Mexican cattle baron Señor Vidal, [Donald Randolph]. When Vidal learns of the romance, he orders Harris to stay away and plans to take his daughter back to Mexico.
Meanwhile, Tom Reese, [Glenn Ford], finishes a cattle drive and takes over an entire wing of the hotel as is his habit. He negotiates to buy cattle from Vidal in Mexico, but when Reese loses his money in a poker game, Harris sees a chance to better himself and to see Maria again, offering his entire life savings to become a partner in Reese's next drive, with profits to be shared 50:50.
The next morning, Harris arrives, and Reese tries to back out, reluctant to partner with an inexperienced hand. But Harris insists on honoring their deal, and they set out toward Vidal's ranch, where the rough realities of trail life begin to test him. One of the hands is killed by a rattlesnake bite during a reckless moment between two other hands, a tragedy that hardens Harris and slowly earns Reese’s respect.
When they reach Vidal's ranch, Harris is crushed to learn that Maria has been married off by her father to Don Manuel Arriega, [Eugene Iglesias]. Arriega warns Harris to stay away, and at a fiesta, he performs a dangerous stunt—placing a ring on a bull's horn from his horse—and challenges the Americans to imitate. Harris accepts the risk, but Reese intervenes to shield him; Reese confronts the bull on foot and succeeds, sparing Harris from a perilous moment.
On the return to Chicago, Maria's marriage gnaws at Harris, turning him increasingly harsh and distrustful, mirroring the way Reese once treated him. Yet when a Comanche ambush threatens the strays, Reese saves Harris by stampeding the herd to keep them safe, and Harris takes over as trail boss while Reese recuperates from a knee wound. He insists the 200 head lost in the stampede come out of Reese's share, and he drives the men hard. The darker mood thickens when a former US marshal among the hands shoots a friend and then takes his own life, yet Harris presses on with the drive.
Later, a pivotal moment arrives when Reese saves Harris again—this time pulling him from a crowded cattle car on a train where a lone steer is at risk of being crushed. The act of rescue jolts Harris back toward sense, and he finally proposes that any lost cattle be shared 50/50. Back in the city, the two men celebrate their hard-won venture and, in a surprising turn, take over a portion of the hotel where Harris once worked, much to the shock of his former boss.
