In 1959 South Dakota, 15-year-old Holly Sargis is a teenage girl living in a dead-end town called Fort Dupree. She lives with her sign painter father, although their relationship has been strained since her mother died of pneumonia some years earlier. One day Holly meets a 25-year-old garbage collector named Kit Carruthers. Kit is a young, troubled greaser and Korean War veteran, who resembles James Dean, an actor Holly admires. Kit charms Holly, and she quickly falls in love with him. As Holly falls deeper in love for Kit, his violent and anti-social tendencies start to slowly reveal themselves.
Holly’s father disapproves of Holly and Kit’s relationship and shoots her dog as punishment for spending time with him. Kit then comes to Holly’s house and shoots her father dead. The couple fakes suicide by burning down the house and go on the run together, making their way towards the badlands of Montana. Kit and Holly build a treehouse in a remote area and live there happily for a time, fishing and stealing chickens for food, but are eventually discovered by bounty hunters. Kit shoots the three bounty hunters dead, and the couple flees. They next seek shelter with Kit’s friend Cato, but when Cato attempts to deceive them and go for help, Kit kills him as well as a teenage couple who arrive to visit Cato shortly thereafter.
Kit and Holly are hunted across the Midwest by law enforcement. They stop at a rich man’s mansion and take supplies, clothing, and his Cadillac, but spare the lives of the man and his housemaid. As the fugitives head across Montana to Saskatchewan, the police find and pursue them.
Holly, who is tired of life on the run and of her relationship with Kit, refuses to go with him and turns herself in. Kit leads the police on a car chase but is soon caught, and enjoys the attention he receives from police and reporters. The crowd engages with Kit as he is waiting in their custody, asking him questions and cracking jokes. Kit is later executed for his crimes, while Holly receives probation and marries her defense attorney’s son.