Set in a future England (ca. 1995, imagined from 1965), the film follows the life of a fifteen-year-old boy named Alex de Large whose pleasures are classical music (most especially Beethoven), rape, and ultraviolence. He is leader of a small gang of thugs, whom he refers to as his "droogs". Alex narrates most of the film in "nadsat", the fractured, contemporary adolescent argot comprising Slavic (especially Russian), English, and Cockney rhyming slang. The boy Alex is irreverent and abusive of others; he lies to his parents to skip school; has an expensive stereo sound deck blasting a classics recordings collection.
After drinking narcotic-laden milk at the Korova Milk Bar, Alex and his droogs beat an old drunken tramp (an Irish immigrant) under a freeway overpass. They then proceed to an old derilect casino where a rival gang led by Billy Boy are about to rape a woman and a fight between the two sets of boys begins. Alex is victorious.
Alex leads his droogs in a home invasion, beating a writer and raping his wife while singing and dancing to Singin' in the Rain. While skipping school for the day, he picks up two teenyboppers in a record shop, takes them home, and hurriedly has sex with both to strains of the William Tell Overture. (In 1971, there was journalistic controversy about whether this scene constituted "obscenity" or not.)
Alex is soon faced by an attempted coup by one of his subordinate droogs, Georgie. Alex is slightly threatened, but seemingly deals with the problem, he kicks the droog into the bay as they walk along the "flatblock marina", and cuts the top of his wrist. He thus proves his leadership and unwillingness to be overthrown.
That night, Alex is caught during a burglary, a mutinous set-up by his ill-contented droogs. Alex breaks into a woman's house and uses a ceramic phallus to beat (and accidentally kill) the owner. Alex is then attacked by his droogs and left helpless at the scene of their crime to be caught by the police. After being arrested, he learns that his robbery victim has died: Alex is a murderer. He is sentenced to 14 years in prison.
After serving two years, he is offered a chance at parole if he submits to the Ludovico technique, an experimental aversion therapy developed by the government to solve societal crime. The technique involves being exposed to extreme depictions of on-screen violence under the influence of a nausea-inducing drug. Alex is unable to look away from the screen, each of his eyes held open by a speculum.
AlexConsequently, Alex is rendered incapable of violence, even in self-defense, and also incapable of touching a naked woman during a test of the technique, crawling away retching. Sadly, in an unintended side effect, the Technique has also rendered him averse to Beethoven's Ninth Symphony, the background score in one of the films; the scientist-doctors apologise: "It can't be helped", saying that musical aversion is "the punishment element, perhaps?"
Once Alex has successfully completed the therapy, he returns home, joyful at the thought of starting afresh. However, he is unpleasantly surprised by the discovery that his parents have rented out his room to a new young man, essentially "replacing" their son. So with no place to go, stripped of the ability to defend himself, Alex despondently wanders London with his few belongings from the prison. He soon encounters the Irish tramp who, with his street friends, attacks the defenseless boy. He is then discovered by two former droogs, now policemen, who take him into the outskirts of town to beat him and nearly drown him.
Alex wanders through the woods and unwittingly arrives upon the house of the writer whose wife he had raped and beaten earlier in the film. The writer takes him in before discovering his identity; subsequently, he then drugs Alex and attempts to drive him insane with an electronic version of the Ninth Symphony (Second Movement) played at full volume below Alex's locked bedroom. The boy attempts suicide by jumping out a window, but survives. As a result of this conquering of the fear of death, Alex inadvertantly cures himself of his crippling psychological anguish.
During his long recovery in hospital, Alex is visited by the Minister of the Interior who earlier had personally selected Alex for the Ludovico Technique treatment. He apologises to Alex for the treatment's consequences, saying he was only following his staff's recommendations. He begins politically seducing Alex by presenting him with an enormous stereo playing the Ninth Symphony's finale (Fourth Movement), which Alex harkens with no physical reaction.
The government promises Alex a job if he agrees to campaign on behalf of the ruling Conservative political party, whose public image has been severely damaged by Alex's attempted suicide. Anticipating his return to havoc, Alex relives his surreal fantasy of having sex with a woman in the snow, surrounded by applauding Victorian ladies and gentlemen. With the finale of Beethoven's Ninth Symphony in the background, Alex narrates the film's end: "I was cured, all right..." .
