In St. Joseph, Missouri in 1886, young law student Jack Slade is taunted by his professor about his late father, after whom Jack was named. The elder Slade was notorious for his quickness with a gun, and the professor alleges that he used his status as a lawman to murder legally. Jack intimidates the professor with a pistol then storms off to the countryside, where he practices his own fast draw. Jack's skill is witnessed by a passing stranger, Joseph Ryan, who reveals that he is a Pinkerton detective who knew Jack's father. Ryan assures Jack that his father was a good man serving his country, not a cold-blooded killer. Ryan also tells Jack, who asserts that he is giving up his law studies, that the detective agency could use him in their attempt to apprehend the infamous "Wild Bunch," led by outlaws Billy Wilcox, Harry Sutton, Kid Stanley, Little Blue Raeburn and George Hagen. Ryan gives Jack a photograph of the gang, which was taken one day while they were drunk, and encourages the young man to meet him in Casper, Wyoming if he wants the job. Soon after, Ryan writes to the still-undecided Jack, telling him that he can use his gun for right or for wrong, and Jack determines to become a lawman like his father. During the train journey to Casper, Jack makes the acquaintance of Johnny Turner, an affable, drunken cowboy. The next day, the train is robbed by the Wild Bunch, and Jack is surprised that one member of the gang is a lovely blonde who takes his Colt .45. At the next town, after Jack buys a new Colt and a two-gun holster, he informs Johnny that he is going to the Hole-in-the-Wall, the gang's hideout, to retrieve his firearm. Johnny wants to accompany him, but Jack, unwilling to entangle Johnny in his dangerous mission, knocks him unconscious to prevent him from following. At Casper, Jack finds Ryan, who orders him to infiltrate the gang and learn how many people are living at the Hole-in-the-Wall, a narrow gorge that leads out to a valley. The hideout is a veritable fortress, filled with outlaws and wandering cowboys, and Ryan needs accurate reconnaissance before the Pinkertons can invade. As Jack is riding out of town, he runs into Sutton, who is drunkenly terrorizing a store owner. Jack humiliates Sutton by shooting his gun out of his hand, and the outlaw vows revenge. Upon arriving at the Hole-in-the-Wall, Jack is interrogated by Billy, who is bemused by Jack's insistence that he came to retrieve his gun. The blonde bandit, known as Texas Rose, recognizes Jack from the train holdup and offers to return his gun. Jack also states that he is there to settle a score with Sutton, and Billy allows him to stay and Texas to return his gun. Later, Jack is outraged when Sutton rides into the hideout with Johnny tied behind his horse. Johnny, almost dead from having been forced to walk for miles, is tended to by Texas and another woman, Polly Logan, while Jack and Sutton prepare to shoot it out. Sutton is obviously drunk, however, so Jack orders him to drop his weapon, and his fast shooting, which propels the gun across the ground, deeply impresses Billy. Billy decides to include Jack in the next day's robbery of a buckboard carrying $15,000, and the next morning, Texas and two other women, Laughing Sam and Abilene, act as decoys to stop the wagon. The men then take the cash, although Jack prevents Abilene from robbing one of the passengers, a preacher. Sutton wantonly shoots the guard, even though Billy had warned him that there was to be no violence. Afterward, at the cave, Johnny awakens when the picture of the gang, with descriptions of each man on the back, falls from Jack's pocket onto his bunk while Jack washes up. Johnny holds onto the photo and Jack is prevented from retrieving it by the arrival of Stanley, who shares their crude quarters. Later, Jack meets Ryan at a saloon in town and informs him that the outlaws are too numerous for the Pinkertons to invade the hideout. Jack advises Ryan to lay a trap for Billy, and Ryan instructs him to bring some of the gang members back to the saloon in two nights. While Jack is gone, Sutton discovers the photograph in Johnny's possession and accuses him of being a Pinkerton agent. Johnny refuses to implicate Jack, and Sutton sadistically forces him to run barefoot across the rocks before shooting him in the back. When Jack returns, he is heartbroken to learn of Johnny's death, and promises Johnny that the outlaws will die because they killed him. The next day, Texas, who has fallen in love with Jack, attempts to comfort him, and he confesses that he loves her, too. That night, Texas, Sutton and Stanley ride with Jack to the saloon, where Ryan pretends to be a drunkard recently fired by the railroad. Ryan states that a major gold shipment will go out in the morning, and the information is relayed to Billy, who decides to rob the train but orders the women to remain behind. Texas, determined to be with Jack, follows the men anyway, and in the morning, when the ambush commences, watches as Jack joins forces with Ryan and the other Pinkerton men manning the train. The detectives order the outlaws to throw down their weapons, but Billy, infuriated by being deceived by Jack, calls him out for a duel. As the men are preparing to draw, Sutton sees Texas riding toward them and shoots her off her horse. While Jack is distracted, Billy attempts to shoot him, but Jack kills him first. Jack then dives under the train for protection as a gun battle between the outlaws and detectives breaks out. The lawmen are prevailing as Jack crawls over to the wounded Texas and lifts her onto her horse. Sutton and Hagen then chase after Jack and Texas while the Pinkertons round up the remaining outlaws. Jack hides with Texas in a cave, then succeeds in gunning down their pursuers. Although Texas is seriously wounded, she smiles at Jack and assures him that she can make it to the nearest doctor, telling him "Wherever you go, I go."