As rancher Dan Evans and his young sons, Mathew and Mark, watch helplessly, outlaw Ben Wade and his gang rob the Butterfield stage and kill its driver, Bill Moons. After the charming yet deadly Wade confiscates Dan and his sons’ horses, Mark asks his father why he failed to resist the outlaws. Later, at home, Dan’s devoted wife Alice expresses incredulity over her husband’s lack of outrage over the crime, prompting Dan, defeated and distracted by the drought that threatens his ranch, to vow that he will obtain the $200 that a neighboring rancher is demanding for access to a spring running through his land. At a saloon in the nearby town of Bizby, Wade and his men, posing as cowhands, tell Emmy, the pretty bartender, that they just witnessed the stage being robbed and its driver killed. After the marshal organizes a posse and rides out after the outlaws, Wade’s men scatter into the countryside while Wade remains behind to romance Emmy. When the posse encounters Dan along the trail, he identifies the perpetrators as the Wade gang. Alex Potter, the town drunk, later catches up to the posse and announces that Wade is still at the saloon, after which they ride back to town to capture him. As Dan distracts Wade by demanding that he pay for his lost time, the marshal sneaks up from behind and arrests him. Witnessing the arrest, one of Wade’s gang rides out to notify the others of Wade’s peril. Aware that the outlaws will return to free their leader, the marshal offers $200 to any man who will take Wade to trial. His only takers are Dan and the inept Alex. The marshal then puts Wade on the next stagecoach headed out of town. While Wade’s men watch from the hills above Dan’s ranch, the stage appears to break down, and as the men struggle to free it from a rut in the trail, Wade is surreptitiously removed and replaced by an imposter, thus fooling the outlaws. Wade is then held prisoner at Dan’s ranch, and after dark, Dan and Alex escort him to Contention City, where they are to put him aboard the 3:10 train to Yuma. At daybreak, they reach Contention City, where Mr. Butterfield, the owner of the stage line, has rented a room for them at the hotel. As Alex watches the street and Butterfield questions the desk clerk about a customer sleeping under a newspaper in the lobby, Dan guards Wade upstairs in the bridal suite. Dan threatens to shoot if Wade tries to escape, but when Wade tries to jump him, Dan relents and spares his life. Gradually, Dan becomes unnerved by the smooth-talking Wade, who offers him $400 to let him escape. As they peer out the window, Moons’s funeral procession passes, prompting Wade to assert that he shot the driver in self-defense. When the funeral procession enters the saloon, Moons’s drunken brother Bob sees Butterfield and denounces him for not attending the funeral. After Bob forces Butterfield to reveal that his brother’s killer is upstairs, Bob breaks in the door to the bridal suite, determined to kill Wade. Dan protects Wade, but in the ensuing struggle, Bob’s gun fires, alerting the customer Butterfield noticed sleeping in the lobby, Wade's henchman, Charlie Prince. Spotting Wade through the hotel room window, Charlie mounts his horse and gallops off for reinforcements. After Dan learns that the sheriff is out of town and therefore unavailable to help him combat the outlaws, Bob cowardly refuses to become involved and quickly departs. At 2:30, Butterfield arrives with news that he has recruited five men to join their cause. As Wade continues to rattle Dan by listing the many sacrifices that Alice has made for him, thus implying that he has been a bad husband, Alex warns that the gang is nearing town, and Butterfield positions his men in the lobby. When the gang reaches the hotel, Wade warns Dan that he may never see Alice and his sons again unless Dan frees him. After Butterfield’s men desert in fear, Wade further undermines Dan’s confidence by stating that Butterfield will walk out on him, too. When Alex alerts Dan to a sniper on the roof, Charlie shoots the hapless drunk in the back. Butterfield then runs to Dan’s room, and they look on in horror as Alex’s dead body is hung from the lobby chandelier. Panicked, Butterfield releases Dan from his obligation. As thunder begins to rumble ominously in the background, Alice, concerned about her husband, drives her carriage into town and enters the hotel. After passing Alex’s body, Alice runs into Dan’s arms and begs him to quit. Dan fervently replies that if the town drunk can give his life for justice, so can he. When the clock strikes three, Dan asks Butterfield to drive Alice to safety while he escorts Wade out the back door. As a whistle signals the train’s approach, one of Wade’s men fires at Dan but misses. When he sees a herd of cows filing down the street, Dan uses them as cover and runs toward the station. As the train starts to pull out, the gang emerges from behind the billowing smoke and Charlie urges Wade to run so that he can have a clear shot at Dan. Wade refuses to budge, however, and unexpectedly agrees to follow Dan’s orders and jump into the passing baggage car. Once inside, Wade explains that he owed Dan for saving his life back at the hotel. As the train passes Alice waiting by the tracks in her carriage, Dan waves at her and it begins to pour.