London, England, the foreseeable future, c. 1995. "Our humble narrator" Alexander DeLarge (Malcolm McDowell) and his droogs, Georgie (James Marcus), Dim (Warren Clarke), and Pete (Michael Tarn), are seated in the Korova Milk Bar stoned on milk laced with narcotics. The gang leaves the Korova for a night of fun.
They encounter an Irish wino (Paul Farrell) in a concrete subway tunnel under a local motorway. They beat him with their truncheons. Later, they arrive at a derelict casino.
On the stage, another gang, led by a schoolmate named Billy Boy, is preparing to rape a voluptuous girl. Instead, the two gangs have a battle in which Alex and his droogs are victorious.
Alex and his droogs next head out into the dark countryside looking for action. Alex pilots their stolen Durango 95 sports car. After playing "hogs of the road", driving on the wrong side of the road and running a number of other travelers into ditches and over embankments, Alex suggests making the "surprise visit".
Stopping at a fancy country house that displays a backlighted sign that simply reads: "Home", they trick their way into the house.
They beat its owner, a writer named Frank Alexander (Patrick Magee), and gang rape his wife (Adrienne Corri) while Alex brightly croons Singin' in the Rain.
The gang returns to the Korova. A woman seated at an adjacent table sings the chorus from Beethoven's 9th symphony. Alex is ecstatic "I felt all the malenky little hairs on my plott standing endwise," but Dim makes a farting noise. Alex hits him in the crotch with his truncheon. Henceforth, Dim is resentful and threatening, but Alex dismisses him.
Dawn is nigh as Alex arrives at his apartment. Before going to bed he fantasizes scenes of violence while listening to Beethoven's Ninth symphony. In the morning, Alex's mother (Sheila Raynor) tries to wake Alex for school, but he feigns illness.
At the breakfast table she discusses the situation with his father (Philip Stone). Alex's parents seem foolish and impotent to his antics and shenanigans.
When Alex later wakes up and wanders about the apartment in his underwear, he encounters his probation officer, Mr. Deltoid (Aubrey Morris), in his parent's bedroom. His mother had given Deltoid a key.
The officer lectures Alex about his truancy from school and threatens him with jail. Deltoid is abashed when he discovers that, in addition to water, the bedside glass from which he's been drinking also contains a set of dentures.
Alex begins another busy day. Alex picks up two girls at a local shopping mall record store and brings them home. In a sped-up sequence backed by the William Tell Overture, he has sex with both of them.
Later that day, he encounters his droogs in the apartment house lobby. They say they've been talking. They're angry with Alex's abuse of them, particularly Dim, and suggest that Alex has been taking more than his fair share of the spoils of their robberies.
Georgie has an idea to make lots more money. He wants to rob a rich lady who owns an upscale health farm at the edge of town. Alex perceives Georgie's independent thinking as a threat but appears to go along with it.
He then unexpectedly attacks his droogs as they walk along a river bank outside the apartment block. He throws first Georgie and then Dim into the dirty river water.