Henry Miller, a fictional version of the author, has been sent by his wife, Mona, to live in Paris and become a writer. He spends much of his time financially destitute, staying at the houses of friends. What little money he gets from his wife, Mona, gets squandered on alcohol and prostitutes, causing him to go hungry, often having to search for people and restaurants that will feed him for nothing. He wanders the streets of Paris, flooded by the sensations of the city and pondering what he believes is the death of Western civilization, which is rotting from within. His poverty may be difficult, but it serves a purpose. Henry has an unquenchable vitality, a true lust for life, equally embracing its horrors and its beauties and advocating, above all, personal freedom. This view of existence is the essence of Henry's growth and development as an artist.
Mona, whose character is based on one of author Henry Miller's wives, June Mansfield, never shows up to visit Henry in Paris. He only remembers her last visit, in 1928, but he longs for her throughout the novel. During Mona's last visit to Europe Henry cheats on her with a random woman in the bathroom of a bar. Mona and Henry wander the streets of Paris, have a lot of sex, and end up sleeping in a hotel room infested with bugs. Mona never returns, likely because she is the kind of woman Henry says wants to be poor in a romantic way, meaning living somewhere with a garden and indoor plumbing, which doesn't mean being poor at all. Back in the United States, Mona suffers from poverty, yet sends Henry money whenever she can. The last Henry hears about Mona, she is starving and ill. Henry chooses not to go back to America and help Mona, but stays in Paris, eventually getting over his love for her.
Van Norden works for the newspaper and eventually gets Henry Miller a job as a proofreader. Van Norden proves to be a ruthless, opportunistic misogynist, who denigrates women to empower himself. One night Henry watches Van Norden have sex with a prostitute, an act spurring Henry's realization that sex is like war, and mechanical sex without emotion is inhuman and meaningless. Van Norden claims he wants to find a woman he can love, a woman he thinks is better than he is, but he also admits he's too egotistical to do so. Van Norden's philosophical views cause him to be continually pessimistic and depressed. At the end of the novel, Henry reconnects with Van Norden again, but Henry is amazed to discover Van Norden's new hobby is masturbating into hollowed-out apple cores.
Fillmore, an American diplomat much younger than Henry Miller, has a soft spot for down-and-out women and men. Fillmore's wealth gives Henry a comfortable place to stay, and a steady income, and changes the nature of Henry's writing. A good influence at first, Fillmore takes Henry to Le Havre for a wild weekend, which improves Henry's outlook on life. Fillmore and Henry split up for several months, and when Henry returns, he finds Fillmore has come apart, landing himself in a mental hospital with syphilis and "delusions of grandeur"; and everyone believes Fillmore is crazy. He's gotten a local French girl, Ginette, pregnant and infected with the clap. Ginette abuses Fillmore when he gets out of the hospital, and ultimately breaks his spirit. Henry tries to get away from Fillmore and Ginette, but when he runs in to Fillmore and sees how he's fallen apart, Henry takes it upon himself to save his friend. Fillmore scurries out of Paris and heads back to America, leaving pregnant Ginette without support. Henry promises to give Ginette money from Fillmore, but Henry keeps the money all to himself.
Boris, possibly a psychoanalyst, houses Henry Miller in the beginning of the novel. However, Boris won't eat in front of Henry because it makes him feel guilty. And, although Boris has a lot of money, he thinks he can't share with Henry in case something happens in the future. Boris and Henry work on a book together, something they believe will be more important than the Bible, and they spend a lot of time with the Tania, Sylvester, and Moldorf crowd. Boris has a wife somewhere, but he hides from her. He wants to escape his life with her, but he is too afraid to do anything about it. Henry stops spending time with Boris early in the novel. Months later Henry receives an unintelligible letter from Boris, revealing how nihilistic Boris is. Henry rejects Boris's views on Henry and life in general, and Boris fades out of Henry's life.
Carl, one of Henry Miller's closest friends, hates optimism, hates Paris, and has a melancholy disposition that, at times, Henry struggles against. Henry laughs at Carl, who provides a big weekly spread for Henry on Carl's days off. Carl and Henry, together, take over Marlowe's review at the paper. Described as "tiny ... frail ... [and] romantic looking," Carl is terrified at the thought of having sex with an older woman he's been writing letters to. Unlike Henry, Carl can't stand the idea of using someone sexually for money. Carl has a nervous, suicidal disposition, and mentions he'd like to go back to America. During a long absence from Henry, Carl changes when he falls for a 15-year-old French girl and gets caught. He still holds down his newspaper job at the end of the novel, but he's more sexually loose and romantic, having revealed and fulfilled a desire for young, illegally aged girls.
Tania, likely based on the real Anaïs Nin, has a long emotional and physical affair with Henry Miller, behind her husband Sylvester's back. Tania enjoys holding the affair right under her husband's nose, and seems to use the two men's jealousy to fuel her flair for the dramatic. Tania and Henry's affair turns serious, and she encourages him to move to Russia with her. She wants to make love to Henry all the time, but as much as she falls for him, she refuses to help him out financially past a certain point and will not let him live with her. She also ends up describing Henry as "cancer and delirium," implying there are some characteristics she does not like about him. When the relationship gets too serious, Henry allows Tania to fade out of his life.