A Clockwork Orange unfolds in the dark and chilly streets of a futuristic city. Alex, the 15-year-old leader of a violent teenage gang, narrates to us in an odd slang (nadsat, it is called) which takes some learning in the beginning.Alex introduces his entourage of criminals – Peter, Georgie, and Dim – and proceeds to take us on an eye-opening journey of ultra-violent crimes inflicted upon helpless innocent people. After boozing up at two local bars, the intoxicated Alex and Co. go on a rampage involving: mugging an old professor, a convenience store robbery, a rival gang fight, grand theft auto, a gang rape, vandalism, and arson. Back at the bar, Alex then gets into a fist fight with Dim and Georgie, who are unhappy with his arrogance. Tired, however, the gang retires for the night, leaving in their wake several hospitalizations, a wrecked car, a good amount of road kill (thanks to their reckless driving), wrecked houses, emotional trauma, and a death.
The next day, Alex plays hooky, gets drunk, and rapes two 10-year-olds to the bombastic music of Beethoven's Symphony No. 9 . At night, he meets up with his friends and proceeds to break into an old woman's mansion to loot it. The police arrive in the nick of time and arrest Alex – just after Dim temporarily blinds Alex in the eye with his chain for payback. Sentenced to 14 years in jail, Alex initially has a hard time adjusting to the climate. Things get easier after two years, though, as he befriends the prison chaplain, takes an interest in the Bible, and is allowed to listen to classical music while doing Bible study.
A new cellmate, a filthy pervert, complicates things. When Alex and the other five cellmates beat their new colleague to death, Alex takes the fall for the murder. Consequently, Alex is chosen by the newly appointed Minister of the Interior to participate in a "reform" treatment called Ludovico's Technique, currently being tested. A behavioral-brainwashing procedure involving elements of associative learning, the treatment program lasts two weeks, after which the criminal is supposedly rendered completely unable to even think of committing crime. Alex is injected with a substance that makes him sick while being forced to watch violent films accompanied by classical music. As he comes to associate bodily sickness with violence, the mere thought of violence becomes so overwhelming to him that he'd rather suffer pain himself than have to think about inflicting pain upon others.
Released back into society as an innocuous person incapable of brutality, Alex returns home to his parents, only to be shooed out. He finds himself contemplating suicide at the public library, but victims of his criminal past find him and beat him up. When the police arrive to break up the fight, they turn out to be his old friends-turned-enemies, Dim and Billyboy, who also take him out to the countryside to get even. Left to die out in the snow, Alex wanders into a cottage; the good-hearted F. Alexander takes him in, bathes him, and feeds him.
F. Alexander turns out to be a political dissident hell-bent on overthrowing the current regime, having lost his wife to the ineffective Government two years ago. As he hears stories about the State's mistreatment of Alex, F. Alexander plans to use Alex as a weapon against the Government. Alex recognizes F. Alexander as the writer-husband of the woman he gang-raped two years ago. It takes a while for F. Alexander to recognize Alex, but he eventually does, by the strange way Alex speaks (his use of the slang language, nadsat).
Alex is locked away by F. Alexander's associates in an apartment. The men blast classical music through the wall, seeking to drive Alex to suicide so as to better indict the Government. Alex, driven mad by the sad side-effect of Ludovico's Technique, jumps from the window of the apartment, but he doesn't die. When he comes to in a few weeks time, the State has undone Alex's Reclamation Treatment, F. Alexander has been locked away, a great job has been lined up for Alex, and the Minister of the Interior makes peace with him by presenting him with a new stereo.
Back to his old self, Alex hangs out with a new gang – Len, Rick, and Bully – that engages in some of the same violent behavior as his old group. Somehow, though, Alex is discontent with his lifestyle. A chance encounter with his old friend, Pete, and Pete's new wife, Georgina, at a local coffeehouse arouses a renewed interest in Alex for a "normal" life. Alex resolves that he wants a wife and son for himself, too, and decides that he'll take steps toward attaining that dream.