Alex, a young English hoodlum, heads a gang of four other young hoodlums. Instead of attending school, he spends his time performing acts of theft, rape, and violence. During the first night of the film, Alex and his gang members, the Droogs, gather at the Korova Milk Bar, which serves its patrons drug-laced milk from female mannequins. They take a drug that makes them hyperaware and ready for violence, then head out into the night and beat up an old homeless man. Next they come upon a rival gang about to rape a woman, and initiate a gang fight. They steal a car and speed out to the country. There, they don masks, burst into the home of a famous writer, Mr. Alexander, beat him, and rape his wife. As Alex rips off Mrs. Alexander’s clothes before the rape, he sings “Singin’ in the Rain” and dances like Gene Kelly does in the musical of the same name. During this night, Alex wreaks havoc in such a happy-go-lucky way that his violence seems motivated by pure enjoyment.
As the night comes to an end, Alex returns to his parents’ apartment in a decrepit working-class housing complex. Before he climbs into bed, he turns on a symphony by Beethoven. The music conjures up images of bombings, hangings, and other forms of violence. In the morning, Alex’s mother wakes him for school, but he says he feels ill. Though he plays the role of dutiful son, his parents clearly don’t dare challenge him.
Soon, however, things begin to unravel for Alex. His Droogs have grown tired of his bullying, and they plan to oust him from power. The next night, they drive out to the home of a wealthy lady. Alex breaks in to rob her, but she fights back. In a surreal scene, she seizes a bust of Beethoven, and Alex seizes a statue of a penis. Just as police sirens begin to sound, Alex smashes her in the face with the statue and runs out. Outside, his friends lie in wait. They hit him over the head with a glass bottle of milk and run away, leaving him to the police.
During the night he spends in police custody, the woman dies, and soon the court sentences Alex to fourteen years in prison. For two years, he behaves like a model prisoner, but he has not truly reformed. What he wants is freedom. One day, Alex hears rumors circulating about a new experimental procedure called Ludovico’s Technique. The government plans to use it to reduce overcrowding in its prisons and to bring law and order to the streets. Alex doesn’t know what the treatment entails, but he is excited to hear that if he undergoes it, the government will release him from prison in just two weeks. When the minister of the interior visits the prison looking for a guinea pig, Alex calls attention to himself and is selected.
Soon, prison officials place Alex in the hands of government doctors, who inject him with a serum, then show him reel upon reel of violent and sexually explicit films. When he sees the films, the serum takes effect, and Alex experiences a horrendous illness, which is brought on by viewing sex or violence. Finally, even without the serum, he automatically becomes ill when he views images of violence or thinks any violent thoughts of his own. His violent impulses are now inhibited by his own physical response. Unfortunately for Alex, one of the films the doctors show him has a soundtrack that he adores: the fourth movement of Beethoven’s Ninth Symphony. As a result, Alex becomes violently ill whenever he hears it. Still, he believes he has gotten a good deal when the government sets him free.
When Alex gets home, he finds that his parents have let his room to a lodger, and they tell him he can’t stay. Outside, the homeless man Alex once beat up recognizes him, and he and his elderly homeless friends attack Alex. The police come to his aid, but they are his old Droogs, criminals now turned cops, and they drive him out to the country and beat him too. Night falls, a storm kicks up, and Alex drags himself to the nearest house. Once inside the house he realizes it’s the home of Mr. Alexander, the writer he assaulted. Mrs. Alexander, whom he raped, had died soon after his attack.
At first Mr. Alexander recognizes Alex only as the boy he’s seen in the newspapers for having undergone Ludovico’s Technique. Mr. Alexander is a member of an opposition political party, and he believes that if he can show that Alex suffered cruelly at the hands of the government, the public may turn against it. He sees in Alex an opportunity to topple the government and takes Alex into his house. While he plans his scheme, Alex, soaking in a bath, begins to feel a little better and starts to sing “Singin’ in the Rain,” the same song he sang the night of the attack. Mr. Alexander recognizes the song, and he makes the connection that Alex is his former assailant. Now he not only wants to use Alex to topple the government but also wants revenge. He hatches a plan to drive Alex to suicide. Later in the day, while Alex sleeps, Mr. Alexander and two cronies blast Beethoven’s Ninth Symphony into Alex’s bedroom. Alex is overcome with illness, but when he tries to flee, he finds his door locked. Desperate to escape his illness, he decides to commit suicide. He jumps from the window.
Alex wakes up in a hospital, after a long time in a coma, in a full-body cast. While he was unconscious, much happened. Public opinion and the newspapers did turn against the government, claiming its cruelty drove Alex to attempt suicide. Mr. Alexander’s plan seems to be working—but the government has a plan of its own. While Alex was in a coma, doctors reconditioned him back to his old self. They have undone the results of Ludovico’s Technique.
The minister of the interior visits Alex in his hospital bed. Alex is eating his lunch, but because the cast confines his movements, he cannot feed himself. In a saccharine gesture of concern, the minister of the interior feeds Alex himself, while Alex slams his mouth open and shut, enjoying his power. The minister of the interior tells Alex how the government plans to help him, with a good job and a good salary. As a final present, the minister of the interior pipes Beethoven into the room, and Alex does not grow ill. The two sit together as journalists and cameramen rush in to capture the moment. As they wave and smile at the cameras, Alex, inspired by the music, imagines himself having wild sex while proper English men and women stand around and applaud. “I was cured all right,” he says as the film ends.