In a strange slang dialect that mixes non-English words and elevated diction, Alex recounts hanging out with his three “droogs,” Dim, Pete, and Georgie. The group decides to rove the streets, and they beat and rob an elderly scholar. Later, the droogs come across a rival gang-leader named Billyboy. After a gang fight, the droogs break into a young couple’s country cottage. They rape the wife in front of the husband and destroy the husband’s manuscript for a book called A Clockwork Orange. Later that night, Alex’s domineering behavior offends his droogs after the droogs don't act respectfully as some music is being performed. They part ways antagonistically.
The next day, Alex skips school. His Post-Corrective Adviser, P.R. Deltoid, visits his house to caution him against misbehaving, but Alex ignores him. That evening, Georgie and Dim inform Alex that they will no longer tolerate his abusive leadership. Alex fights them, prevails, and resumes his role as leader. The boys then decide to rob an elderly woman’s house. Alex breaks into the house. The woman and her cats attack him, and he retaliates brutally. He hears sirens and attempts to escape, but Dim strikes him in the eyes and the rest of the droogs abandon him to be captured. The next day, in police custody, Alex learns that his attack on the old woman has killed her.
Part Two begins two years after Part One. Alex is serving a fourteen-year sentence in the State Jail (“Staja”). In prison, Alex works for the prison chaplain. The chaplain mentions a procedure, which deprives criminals of their ability to choose to misbehave. Later that day, a new prisoner is introduced to Alex’s cell. He tries to molest Alex, and Alex and his cellmates take turns beating him in retaliation. This beating proves fatal, and the other cellmates blame Alex. The Minister of the Interior decides Alex will receive the experimental treatment—Reclamation Treatment—that the chaplain alluded to earlier.
Under the supervision of Dr. Brodsky and Dr. Branom, Alex is given injections and forced to sit through hours of violent films. He is restrained in a chair that makes it impossible for him to close his eyes or turn away from these films, and even though the violence begins to viscerally sicken him, the doctors simply subject Alex to film after film. One film, which plays Beethoven’s Fifth Symphony over footage of Nazi war crimes, makes Alex especially furious, because it causes him to associate his favorite music with visceral sickness. Finally, Alex is ready for release. He is brought in front of an audience and assaulted, but his aversion to violence makes him unable to fight back.
In Part Three, Alex returns to his home and finds that his parents have replaced him with a lodger named Joe. Homeless, Alex resolves to kill himself. By chance, he is spotted by the scholar he assaulted years earlier. The old man and his friends beat Alex until police arrive to break up the fight. Dim and Billyboy are among the responding policemen, and they take Alex to the countryside, rape him, and abandon him. Alex unknowingly returns to the same cottage he ransacked with his droogs, and the male homeowner—not recognizing Alex—takes him in and nurses him back to health.
The homeowner is named F. Alexander, and his book A Clockwork Orange is a polemic against Reclamation Treatment. He hopes to use Alex as a political device to further this agenda. Some of his cohorts take Alex to an apartment. There, Alex is locked in a room and forced to listen to classical music; the pain is so great that he jumps out a window in a suicide attempt. Alex wakes up in the hospital to find that he has received a blood transfusion, which has nullified his Reclamation Treatment. In the hospital, he finds out that F. Alexander has been imprisoned because the author, after realizing that Alex was responsible for the lethal rape of his wife, made threats on Alex’s life. Alex then returns to his old lifestyle with a new group of droogs. However, he is less interested in causing violence and mayhem than he was when younger. After reencountering his former droog Pete, who now lives a tame, married life, Alex decides that he has grown up, and wishes to settle down and live harmlessly.