Frederick is a lonely clerk in his twenties who uses his free time to collect butterflies and bet on the soccer pools. After winning a massive fortune, he quits his job, moves to London, and buys an isolated seventeenth-century cottage with a hidden cellar. Deeply insecure about his social class and disgusted by conventional sexuality, he uses his wealth to orchestrate the abduction of a woman he has watched from afar for a year.

Miranda is a twenty-year-old art student from a comfortable bourgeois family. She actively rebels against the conservative expectations of her parents, preferring the progressive ideals of the 1960s cultural revolution. Suddenly trapped in a subterranean room by a stranger, she relies on her intelligence and sharp tongue to analyze her captor and plan an escape.

George is a forty-one-year-old painter living in London. He is fiercely dogmatic about art, entirely rejecting abstract painting and openly criticizing Miranda's work as derivative. Despite his reputation as a misogynist and a cynic, he exerts a massive intellectual pull on Miranda, who views his cluttered studio and harsh opinions as the height of artistic authenticity.

Annie is Frederick's working-class aunt and guardian. A Nonconformist Christian with a deeply cynical view of the world, she frequently disparages Frederick's interests and warns him about the ulterior motives of young women. She moves to Australia with her daughter, inadvertently giving Frederick the privacy he needs to execute his kidnapping plot.

Dick was Frederick's uncle and surrogate father following the death of Frederick's biological father. He introduced Frederick to butterfly collecting and took him fishing. His sudden death when Frederick was fifteen abruptly ended the happiest period of the boy's life.

Mabel is Frederick's cousin, who lives with disabilities. She accompanies her mother Annie on a long trip to Australia following Frederick's lottery win.

Caroline is Miranda's aunt, a woman deeply embedded in the London art scene. Miranda views her as a somewhat pretentious art collector who chases trends, though Caroline accurately recognizes George Paston's unsavory reputation with women.

Crutchley is a clerk who works alongside Frederick before the lottery win. He is flirtatious and popular with women in the office, qualities that disgust Frederick.

Minny is Miranda's younger sister. She remains at home with their parents, and Miranda frequently thinks of her while enduring her isolated imprisonment in the cellar.

Carmen is a friend of Miranda's from before her abduction. She is a pragmatic young woman who argues that physical realities often override intellectual ones.