In the 1920s, twenty-five-year-old amateur boxer Charles Arthur Floyd, nicknamed "Pretty Boy" for his handsome face, is carrying on an affair with Gail, the wife of promoter Mike Clouder. When Mike learns of the dalliance, he fights Charlie, underestimating the younger man's strength and brutality. After beating him severely, Charlie commands Gail to tell her husband that she loves him in order to win him back. Despite this, during Charlie's next boxing match, Mike spikes his water with an acid that clouds his eyes, allowing his rival to beat him mercilessly. Backstage, trainer Al Riccardo warns Charlie, who has served five years in prison for robbery, not to seek revenge, and offers to train him as a pro boxer. Believing he is too old to begin a fighting career, Charlie hopes instead to earn a promotion to foreman at his day job at the oil fields, but his ambitions are dashed after the oil field boss discovers his prison record. Although Charlie argues that he made a youthful mistake and served his punishment, he is fired, and bitterly packs to return to his hometown of Salazar, Oklahoma. When Gail visits to beg him not to leave, he takes the money she offers, then slaps her. In Oklahoma, his cousin, Jed Watkins, greets him with the news that Charlie's father has been shot to death by neighbor Grindon, who claimed self-defense even though Pa had no gun. Charlie is furious that Grindon was acquitted of murder by his old friend, Sheriff Blackie Faulkner, who years earlier turned Charlie in on the robbery charge after the then-married Charlie seduced Blackie's fifteen-year-old sister. Although Blackie now warns Charlie not to take the law into his own hands, Charlie determines to avenge his father. Over the next days, Charlie reconnects with an adoring young friend, Curly Winwell, and witnesses first-hand the desolation of the "Okies," who have been hit hard by the Depression and drought. His own attempts to rebuild the family farm are stymied when he cannot secure a loan for seed, and his anger builds. One day, Charlie learns of Grindon's whereabouts and, after bludgeoning the man to death, discovers he enjoys the sensation of killing. He flees to Kansas City and joins up with his old cellmate, Shorty Walters. They rob a bank, but when Shorty drunkenly boasts about the job, a hotel clerk alerts the police, and Charlie is arrested. He is sentenced to twelve-to-fifteen years in the Ohio State Penitentiary, but while being transported, kills his police escort and escapes. Returning home, Curly hides him and his other friends supply him with guns. Blackie soon discerns Charlie's whereabouts, so Charlie brazenly strides into town, locks Blackie in the jail and robs the bank. After Charlie distributes the loot to all his friends, he is dubbed "The Sagebrush Robin Hood," and the governor calls in federal agent Neil Trane to launch an investigation. Neil meets with Blackie, who advises that they can stop Charlie only if his friends can be turned against him. Meanwhile, in Kansas City, Charlie meets hoodlum Baker, who introduces him to petty criminal and boardinghouse matron Ma Parks. Also living at Ma's are Bill and Ann Courtney, Bill's brother Ed and Ed's wife Lil. When con artists Bill and Ed soon leave to pull yet another small-time con, Lil and Charlie fall in love. One day, Bill and Ed return with the news that there is a $1,000 reward for Charlie. They instruct their wives to invite him to a fair the following evening, where the police will be waiting to arrest him. Lil, however, tips off Charlie, and with Baker's help, he murders the brothers. Charlie, Baker, Lil and Ann, who are unaware that Charlie has killed their husbands, take off together for Ohio. There, they case a bank, but a nervous Charlie shoots a guard, and in the ensuing shootout with the police, Baker is killed. Charlie sends the women back to Kansas City, despite Lil's pleas to stay with him, and retreats once again to the Oklahoma hills. There, he teaches an overjoyed Curly how to accompany him on holdups, and proceeds to rob banks almost weekly, distributing the money to impoverished farmers. As the newspapers tout Charlie as a living legend, he grows arrogant, sending a note to the governor demanding the reward on his life be withdrawn. Although Blackie and Neil conspire to trap Charlie, he continuously outsmarts them, even managing to rob two banks in one day without getting caught. After the double robbery, Charlie plans a large party to celebrate, heedless of the risk. When he drives to the party site, however, the police are there and manage to wound him before he escapes. Curly brings Charlie to Ma's, where a skilled surgeon and Lil's tender care aid in his full recovery. Seven months later, Charlie is anxious to leave the boardinghouse, and when he hears that Curly has been killed while trying to rob a bank on his own, he takes Lil and returns to Ohio. There, his friends are unwelcoming, blaming him for Curly's death. Charlie and Lil move on to New York, where Charlie reconnects with Al, but the three are forced to leave by gang leader Big Dutch, who fears increased police attention. They return to Ma, who introduces them to Machine Gun Manny. Manny hires Charlie and Al to help liberate mobster Jumpy Lasker as he is transported to jail. The plan is carried out at the Kansas City train station, but when the police disguise Jumpy and place him in the driver's seat, Charlie, Al and Manny accidentally murder him, along with four policemen. The botched job is labeled "The Kansas City Massacre," and the three men come under investigation by the Midwest gang bosses. At a makeshift gangland trial, Manny finally admits that he planned the caper in order to kill Jumpy, and while Charlie and Al are set free, Manny is killed. The FBI presses on relentlessly in its pursuit of Charlie, who, after the death of John Dillinger, becomes Public Enemy No. 1. This time, when he, Lil and Al return to Ohio to seek shelter, his old friends rebuff him completely, and the three are forced to hide out in a shack in the hills. Lil tries to tell Charlie that she is carrying his child, but he is distracted when Al grabs a shotgun and runs off. Charlie follows him into the woods and shoots him, unaware that the noise has tipped off nearby investigators. The lawmen call reinforcements and give chase, and Charlie runs for days through the woods. On 22 October 1934, he seeks help from a lonely woman who is instantly enthralled by him, but as he tries to escape in her car, the police close in. A gunshot ensues during which Charlie is shot repeatedly and killed, bringing to a violent close the brutal case of "Pretty Boy" Floyd.