The novel opens with an "Editors' Note," claiming that the following pages were found among the papers of Antoine Roquentin. The pages are presented in a diary format. The Editors suggest that Roquentin began his diary in January 1932, following his return from the Far East, Central Europe, and North Africa. He moved to the seaside town of Bouville in order to write a book about the Marquis de Rollebon.
Roquentin's introductory notes establish his intent to keep a diary. He feels that something has changed in the way he sees objects, but he cannot quite place his finger on exactly what. He hopes that a diary will help him better understand what is going on, specifically, to see, classify, and determine the extent and nature of the change. He recalls an odd sensation while holding a stone a few days earlier, but is not sure whether the odd feeling came from the stone or himself. Despite his feelings of disgust and being afraid of the stone, he is wary of exaggerating the events he records in his diary. Indeed, he soon writes that his odd feelings were nothing but a passing moment of madness and that there is no longer any need to continue with his diary.
Nevertheless, the next entry, dated January 29, 1932, opens with Roquentin's realization that something strange has happened to him. He first thought that it was nothing but a "passing moment" gives way to a permanent feeling of uneasiness around objects and people. He hopes that it is nothing but an "abstract change," but soon begins to worry that he is the one who has changed little by little, overwhelmed by a sudden transformation. He recalls his whimsical decision to leave Vietnam and return to France, terrified that it was actually a precursor to his current state of mind.
The next day, however, he becomes resigned to his fate, realizing that his solitary lifestyle has changed him. He notices that living alone has prevented him from both having friends and simply communicating with other people. When he looks inside himself for answers, he finds nothing. Even when he has sex with Francoise, a local barmaid, very little is said between them: Roquentin feels that he is purging himself of a "certain nostalgia" rather than feeling pleasure. Yet he does acknowledge that he would be lying to himself if he began to think that nothing new has happened to him. When he looks at a glass of beer or a soggy piece of paper lying in the street he is unable to touch them despite his desire to do so. He does not feel free. Thinking back on the strange feeling he had while holding the stone he recalls a "nausea of the hands."
Roquentin attempts to divert his angst with historical research on the Marquis de Rollebon, a mysterious aristocrat who lived around the time of the French Revolution. Yet Roquentin's research begins to bore him. Ten years earlier he had been fascinated with the story of the Marquis, but now feels that he is writing a work of pure conjecture that has nothing to do with the real Marquis at all. His work inevitably returns Roquentin to himself and his emerging disgust at the outside world. Specifically, the changing appearance of objects in the light of the sun makes him feel uneasy. When he tries to focus on the mystery of Rollebon he can't help but look at himself in the mirror, alarmed that he doesn't recognize his own face.
Existentialism is primarily a reaction against the traditional philosophical approach to objective and abstract understandings of human behavior. Instead, existentialists choose to study individual human beings who exist independently of cultures, traditions, and laws. As Sartre stresses in the "Editors' Note," not only have Roquentin's writings not been altered, but they are his personal papers. This establishes the novel's focus on one singular individual through the lens of his most personal documents. As such, they are an accurate reflection of one person and nothing else--the main focus of existentialist thought.
Even though it will take some time for Roquentin to understand exactly what is happening to both him and the objects and people he sees, he has already begun to address the major themes of existentialism: anxiety, suffering, freedom, and self-deception. In writing his diary, Roquentin first intends to objectively study the changes he has observed, much like traditional philosophers, such as Hegel and Kant, would have used the scientific method to solve problems. Roquentin wants his diary to "sees," "classify," and "determine," just like a scientist would study a phenomenon. But this soon proves impossible as the very qualities, or "essences," of objects he seeks to describe no longer make any sense to him. From the rotting piece of paper on the street to the dirty stone he holds in his hands, Roquentin is unable to see, classify, or determine exactly what he is looking at. This leads him to question his free will, since he is unable to touch these objects; he is afraid of something but still not sure what it is.
Roquentin tries to pass off these odd sensations to his feelings of solitude. He worries that living alone has allowed him to hide the truth of his loneliness from himself. He fears that his diary will exaggerate events and later notes that he wrote that "nothing new" had happened to him with a "bad conscience." He soon admits that something causes him to lie to himself since, "I am not in the habit of telling myself what happens to me." Sartre termed this phenomenon "self-deception," which resulted from an individual's inability to cope with their absolute freedom. He believed that human choice is subjective since each individual is different and unconstrained by laws, cultures, and traditions. They are thus free to do whatever they want, but they consequently must accept full responsibility for their actions. Fear and anxiety in the face of this vast responsibility leads individuals to hide both their freedom and responsibility from themselves by lying to themselves. For example, Roquentin tells himself that he is "no longer free."
Roquentin's research on the Marquis de Rollebon is important for three reasons. First, it introduces the relationship between existence and time. Roquentin looks to the past to find a reason for his existence in the present. But so many details about Rollebon remain a mystery that he is confronted with the inaccessibility of the past as well. This second theme leads Roquentin to believe that objectivity is impossible--that nothing can be proved. In fact, he soon feels that his writings about Rollebon are more about himself than the marquis. Third, and most important, the presence of Rollebon introduces the existentialist theme of duality. Sartre used Descartes' method of posing the cogito, the individual's consciousness and the "other" part of himself or herself that observes that consciousness. For example, Roquentin tries to draw as many parallels between the marquis and himself that he can. Even when he looks at himself in a mirror, he thinks of Rollebon looking in a mirror and how they are both unattractive. This duality is reinforced by the similarities in their names as well as the almost analogous spelling of Roquentin and Rollebon's mistress, Roquelaire. Roquentin's dualistic personality allows him to observe himself, but to his horror he does not recognize his own face. The "nothingness" he perceives in his face recalls the anxiety he felt while looking at the glass of beer and the crumpled piece of paper--but exactly what this "nothingness" is still eludes him.