The Newton Brothers are from Uvalde, Texas, which is Matthew McConaughey's hometown.
Brentwood accidentally shoots Dock during the train robbery, but he survives. The group is caught and are sentenced to prison. Louise promises to wait for Willis once he gets out. Many years later, Joe, the last surviving brother, appears on the Tonight Show and tells Johnny Carson their story.
Set in 1919, Willis Newton (Matthew McConaughey) has just been released from prison for a crime he didn't commit. He goes into town and meets two criminals, Slim and Brentwood (Dwight Yoakum), who tell him that the saloon they are in is now owned by an Indian chief who wasn't allowed inside before he bought it. Knowing that the only way out of poverty and to climb the social ladder is to have money, he agrees to join Slim and Brentwood in robbing a bank. The robbery is successful, but Slim is captured while trying to get away. Willis and Brentwood sell off the stolen war bonds they collected to a crooked banker, who then gives them a list of banks that can easily be robbed. In return Willis promises not to rob that bank.
Willis convinces his brothers Joe (Skeet Ulrich) and Jess (Ethan Hawke) to join them, and the four of them start their crime spree. Willis doesn't want anyone to get hurt, so all of the robberies will be at night. Brentwood's use of nitroglycerin will be how they get the money out of the safes. With early success, they group start to hit out of state banks. While in Omaha, they meet their other brother Dock (Vincent D'Onofrio), who wants to join them. Willis also meets Louise (Julianna Marguiles), and they fall in love.
Because of their success, banks are changing their safes to ones that are nitroglycerin proof. As a result, the Newtons and Brentwood decide to start robbing cash transports. An attempted robbery of a transport in Toronto goes badly, and the group escapes but not before they are forced to shoot the guards. Willis decides he's had enough and tells Louise he's through robbing banks and transports. He and the brothers use their cut of the stolen money to start an oil well, but it's a bust and they lose all their money. After telling Louise he's not meant to be "legit", Willis meets with a newly released Slim and they plan to rob a train in Chicago. Willis gets the gang back together and they plan the heist.
Since the hold-up will be at night, the group wear white cowboy hats to stand out from everyone. The robbery is going well until Dock comes up to Brentwood without his hat (it fell off without him realizing it), and Brentwood shoots him, thinking it was a guard. Instead of their pre-arranged getaway plan, Willis demands that Dock be taken to a doctor in Chicago, even though Slim tells him that will mean certain capture. Dock survives his numerous wounds, but the police are able to track down the gang and they are eventually caught.
Slim and the railroad inside man they were working with are tried separately and receive maximum sentences. Thanks to Jess' wild stories during their trial that charmed the jury, the Newton's and Brentwood all receive light sentences. Title cards afterward tell of what happened to each of them after they were released from prison. Louise promised to wait for Willis once he got out, and she did. Brentwood's whereabouts were unknown once he was released, but the Newton's all lived to old age. The movie ends with the real-life Joe, the last surviving Newton brother, appearing on the Tonight Show and he tells Johnny Carson their story.