Gangster Looney McGann, who reads a Wild West magazine as he travels by train to Arizona, is excited to see from his window a man on horseback pursued by a group firing at him. After helping the man scramble onto the train, Looney opens a violin case to reveal grenades, which he and the man, Tom Daley, throw at the pursuers, who soon retreat. Impressed when Tom says he that he is known as "El Diablo," Looney offers to introduce him to his gang, but Tom is not interested. At the border, customs officer Pedro Gonzales learns that Tom, an American, broke up a wedding and stole the bride. He gathers an army of men and boards the train looking for Tom, who hides in the upper berth of a vacant room. Patricia Carter then enters and, after she tells Gonzales that she is alone, begins to remove her clothing until Tom knocks over a bag. When she screams, Tom puts his hand over her mouth and forces her to listen as he explains that the bride was being forced to marry a man she didn't love and that she was "stolen" with her own consent. After Gonzales and his men leave the train, Tom jumps off the train and rides into Delhi, Arizona, where he tells his old pal, Newt Olsen, that his uncle, Jerry Malone, sent him a letter urging him to take over his ranch, which is the largest in the state. After Newt's ornery wife Sally, angry that Newt is drunk and with Tom, fires a rifle at them, they ride to the Malone ranch. At the ranch, Malone has died, supposedly by accident, and John Ross, Malone's attorney and the leader of Looney's gang, plans to have Frank Briggs, one of his men, pose as Tom so that they can inherit the ranch and then start a Ranchers' and Cattlemen's Protective Association. Pat, an undercover agent who is traveling with Ross, secretly attempts to transmit this information via a radio in her bedroom. When Ross tries to act romantic, she shies away, but promises to go away with him as soon as their work in setting up the association is over. Tom and Newt ride up and learn from a servant that Malone has died. After Tom saves Looney from an irate bull, whom he tried to rope, Looney introduces Tom and Newt, whom he calls "Killer Olsen," to the gang. Tom says that he wants to muscle in on their scheme. Ross then sends his men to kill them at night, but Tom and Newt capture the men and lock them in an ice-house. The next morning, Ross capitulates and suggests that Tom pose as Tom Daley and that Pat pose as his wife, so that if Tom meets with an "accident" or double-crosses them, his "widow" will get the ranch. They go to Judge Wilson's home, where the will is to be probated, but the judge is out of town until the morning. Mrs. Wilson, who, it turns out, is Tom's godmother, insists that he and Pat stay the night, to Ross's and Pat's discomfort. Alone together that night, Pat grows fond of Tom and encourages him to pull out of the scheme, while he remarks that she does not belong with the gang. Tom spends the night in the room sleeping on a chair. The next day, as the will is settled, Looney and Newt get drunk and become pals, but Sally shows up, and after she reveals Tom's identity, the gang captures her and Newt. Pat is relieved when she learns the truth about Tom. After Tom is knocked out, Pat tries to call the police on her radio, but Ross catches her and smashes it. He tells his gang to kill the Olsens and Tom. Tom convinces Looney to help "the killer" and his wife escape. Newt, however, refuses to leave Tom, who fights the gangsters with Newt's and Looney's help. After Briggs shoots Looney, the police arrive, and Ross is shot trying to escape. Although Looney tells Newt that he is "hitting the last trail," Newt points out that Looney's belt stopped the bullet. Sally calls her husband a brave hero and promises never to scold him again. Tom kisses Pat and reminds her that according to the deed they filed when they pretended to be married, half of the ranch is hers. She replies that she is recording it.