The film opens with a tense confrontation between two men at a desolate mansion. Humbert Humbert (James Mason), a British professor in his forties specializing in French literature, invades a property that has been thoroughly wrecked after a wild party the previous night. Inside, he encounters the deranged and drunken Clare Quilty (played by Peter Sellers), who is exhibiting signs of severe dementia and seems unable to recognize Humbert. When Humbert confronts him, pointing a gun at him, Quilty becomes frantic, and after a bizarre struggle, he bizarrely remains polite while Humbert fires repeatedly, leading to Quilty’s rather uninterested demise—his last words delivered in an exaggerated English accent.
The narrative then shifts to four years prior, chronicling Humbert's summer in Ramsdale, New Hampshire, a quiet town where he intends to relax before starting his position at Beardsley College in Ohio. During his search for accommodation, he meets the widowed and sexually desperate Charlotte Haze (Shelley Winters), who invites him to stay at her home. Initially reluctant, Humbert is smitten when he lays eyes on Charlotte’s alluringly youthful 14-year-old daughter, Dolores Haze (Sue Lyon), known endearingly as Lolita—a gum-chewing, soda-crazy flirt who captures Humbert's heart.
To cultivate a relationship with Lolita, Humbert reluctantly accepts Charlotte's hospitality and becomes a roomer in their home. However, Charlotte soon reveals her plan to send Lolita to a sleepaway camp for girls. On the morning of her departure, Humbert receives a note from Charlotte confessing her feelings and insisting he must leave the household if he doesn’t wish to marry her upon her return with Lolita. Overwhelmed, he marries Charlotte days later. Yet, disaster strikes when she discovers Humbert's private diary, where he documents his forbidden love for Lolita. In a fit of rage, she threatens to leave with her daughter, only to meet a tragic end when she is struck by a car as she flees.
Grieving the loss of Charlotte, Humbert goes to Camp Climax to collect Lolita, who is unaware of her mother’s death. As a bizarre twist of fate unfolds, a pushy stranger, Clare Quilty (again portrayed by Peter Sellers), inserts himself into Humbert's life, his intent to talk about Humbert’s “beautiful little daughter.” What follows is a clandestine affair between Humbert and Lolita, marked by a series of motels across the United States where they masquerade as father and daughter.
As they navigate through public life, suspicions about their relationship rise, particularly when Humbert enrolls Lolita in high school upon taking his teaching post. Doubts emerge regarding Lolita’s involvement in school plays and her interactions with male peers. Tension escalates when Humbert finds Dr. Zempf, a garrulous man posing as a psychologist seeking to discuss her education and “the facts of life.” Alarmed, Humbert decides to hit the road again with Lolita.
As Humbert drives across the country, paranoia sets in as he suspects they are being trailed by a mysterious car that stays just out of reach. During a flat tire incident, when Humbert attempts to investigate, Lolita’s sudden anxiousness discourages him, and the suspicious car mysteriously departs.
When Lolita falls ill, Humbert rushes her to a small Arizona hospital. Later that night, however, he receives an alarming phone call, only to come back and discover she has vanished with another man claiming to be her uncle. Heartbroken and clueless about her whereabouts, Humbert becomes desperate.
Years pass until Humbert receives a letter from 'Mrs. Richard T. Schiller', Lolita’s married name. She reveals she is now married to a nearly deaf Korean War veteran named Dick and is pregnant and financially destitute. Humbert, heart racing, finds Lolita, now nearing eighteen. Their reunion uncovers shocking truths: Lolita shares that Quilty was the one who abducted her and reveals that he was the man following them all along, duping her mother into a brief affair. Despite the hardships she has endured, Lolita expresses her desire to stay with her new family and declines Humbert's plea to run away together.
In a bid to sever ties and provide for her future, Humbert hands Lolita $13,000—a share from the sale of her mother’s home. Resolutely, he confronts Clare Quilty at his mansion for abusing Lolita, culminating in a violent showdown that echoes the film’s harrowing beginning. The story concludes with a disclaimer revealing that Humbert passed away in prison from a heart attack while awaiting trial for Quilty's murder, leaving behind a tale of obsession, loss, and tragic intertwined fates.
